The Australian-English slang phrase to piss, or to pee, in someone’s pocket means: to flatter someone or to (seek to) ingratiate oneself with someone, to curry favour with someone.

This phrase occurred, for example, in the following two articles published in the Riverine Herald (Echuca, Victoria, Australia):

1-: Of Monday 2^nd April 2001—the cricket umpire Paul Denham was retiring:

Although many of his colleagues believe he is retiring early, Denham wanted to bow out of the game while he still has the respect of players and fellow umpires.
“I don’t regret one year of it,” Denham said. “You’ve gotta like it to do it.
“One of the things I valued most was the friendship and comraderie I had with the players. I don’t want to piss in my own pocket, but I don’t think I made one enemy over the years.”

2-: Of Wednesday 4^th April 2001:

Correction
Monday’s article about retiring umpire Paul Denham contained some errors.
[…]
[…] One paragraph stated: “I don’t want to piss in my own pocket, but I don’t think I made one enemy over the years.”
Denham actually said: “I don’t want to pee in my own pocket, but….”.
It has been pointed out that Denham would never use such language. The quote only was used in the article to show that Denham was not trying to pump himself up or ‘blow his own trumpet’.

Note: Similar to the Australian-English to piss in someone’s pocket, the British-English phrase to piss down someone’s back was defined as follows in Lexicon Balatronicum ¹. A Dictionary of Buckish Slang, University Wit, and Pickpocket Eloquence (London: Printed for C. Chappel, 1811), by Francis Grose (1731?-1791) and Hewson Clarke (1787-1832?):

Pissing down anyone’s Back. Flattering him.

¹ The adjective balatronicum was derived from the Latin noun bălātro/ōnis, which denoted a babbler, hence a jester, a buffoon. This noun was in turn derived from the verb blătĕro, to talk idly or foolishly, to babble, prate.

The earliest occurrences of the phrase to piss, or to pee, in someone’s pocket that I have found are as follows, in chronological order:

1-: From The Joyful Condemned (London: Macmillan & Co. Ltd, 1953), by the Australian author Kylie Tennant (1912-1988):

‘What I want to know is this: Why are all these chaps like Jake and Chigger Harris—’ He stopped, trying to get the right words. ‘Why am I on the castor with them?’ ²
‘Oh, that.’ Harold’s face cleared. ‘Soon’s they knew you was in with Numismata, they all want to piss in your pocket.’

² From castor, meaning excellent, the phrase to be on the castor means to be popular.

2-: From Uni—a groove or a rut?, by Mick Poulos, published in Tharunka (Kensington, New South Wales, Australia) of Tuesday 24^th February 1970—Tharunka is the student newspaper of the University of New South Wales:

Essays become a night-before nightmare. You just pass. The text book will do. You can’t squeeze all the reference material in and after all, the lecturer really digs what’s in the text. He prescribed it. Some of these guys have got a lot of ego investment in their ideas. So, I’ll just piss in their pockets until I get out of here.

3-: From The Outcasts of Foolgarah (Melbourne : Allara Publishing, 1971), by the Australian author Frank Hardy (1917-1994)—as quoted in A Dictionary of Australian Colloquialisms (Sydney University Press in association with Oxford University Press Australia, 1990), by Gerald Alfred Wilkes (1927-2020):

I appeared before him many a time when I worked for the Union. If we piss in his pocket, he’s just as apt to come our way.

4-: From Ambassador to China, published in The Canberra Times (Canberra, Australian Capital Territory, Australia) of Thursday 29^th June 1972:

Canberra has just acquired an ambassador to the People’s Republic of China—he is not ours, of course, but resides here as Malta’s High Commissioner to Australia.
This extraordinary plenipotentiary is Mr J. L. Forace, who has just returned from a 13-day visit to Peking to present his credentials to acting Chairman and Vice-President Tung Pi-wu.
“I love China”, he told us. “When you have two people who like and admire each other they pee in each other’s pocket when they meet. What more can I say?”

5-: From an article about the Australian photographer Rod McNicol (born 1946), by Beatrice Faust, published in The Age (Melbourne, Victoria, Australia) of Saturday 28^th September 1985:

He believes society functions on the myth that everything is all right. Photographers who photograph people in their own environments, recording the faces that the subjects choose to present, are colluding in the myth. “They are pissing in each other’s pockets.”

6-: From the column Stay in touch, by Michael K. O. Cordell, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Thursday 5^th March 1987:

Frank talk
The scene is Singleton on Tuesday afternoon. John Howard is on the country beat trying to beef up the Liberal Party’s popularity and decides to take a look in at the Pub House Hotel. Frank Gore, a wiry, 40-year-old construction worker, is having a beer with his mates. Howard walks in and Gore starts on a diatribe which lasts about 10 minutes. Much shortened, the conversation goes something like this.
Gore: (in a loud voice) (Expletive) hell, it’s Howard. Have a go at these (expletive). If you expect us to vote for you, you’ve got to do a better job mate. I wouldn’t piss on Bob Hawke, he’s the biggest (expletive) slime in Australia. And that’s not pissing in your pocket mate.

7-: From an account of Why Have Book Reviews?, a symposium held at the Tattersalls Club in Sydney—account by Helen Daniel, published in The Age (Melbourne, Victoria, Australia) of Saturday 28^th March 1987:

There was also a lot of talk about spleen, vengeance, collusion, mateship, a literary mafia and, with less sang froid, pissing in relevant pockets. Much of this has been stimulated by a somewhat bemused Gerard Windsor who, at last year’s Adelaide Writers’ Week, suggested that, in this country with its small literary community, reviewing is an incestuous business.

8-: From an interview of the Australian rugby-league player Steve Mortimer (born 1956), who was about to step down as captain of the Canterbury-Bankstown Bulldogs—interview by David Rowlands, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Saturday 9^th April 1988:

Don’t bet brass on this testimonial year for Mortimer (which he oddly calls a “piss in your own pocket year”) being his final.
He could very well back up again if he’s feeling fine and enjoying playing. A decision will be made at the end of this season.

9-: From Brotherly love rules the airwaves, by Alan Ramsay, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Saturday 26^th August 1989:

Hawke’s appearance on the Midday program was made in tandem with Paul Keating, the best straight man in politics. The two of them were supposed to be there selling the Budget. What they sold was each other. The mateship was trowelled on as thickly as it had been in Don Chipp’s studio.
They peed in each other’s pocket, cracked jokes, belted the pilots, polished one another’s humanity, and did everything but have a cuddle to show how close they were.

10-: From an interview of the Australian radio and television presenter Clive Robertson (born 1945)—interview by Kevin Sadlier, published in The Sun-Herald (Sydney, New South Wales, Australia) of Sunday 1^st April 1990:

ROBERTSON: The only television I’ve really enjoyed in recent years has been the Johnny Carson Show and the David Letterman Show. They are both very clever and they both have a certain dignity we don’t seem to have in Australia. I remember some young performer came on the Carson show and said: ‘Mr. Carson, it’s so wonderful you’ve let me come on your show. I’ve admired you for years. And he said: ‘Thank you.’ Now in Australia they’d say: ‘Oh couldn’t you get on any other show.’ We shoot ourselves in the foot. There is this inferiority complex which we are feeding like billyoh at a time when we should be productive. I don’t understand it, I really don’t. I never want to hear anyone in this country ever again say: ‘I don’t want to piss in your pocket.’ A compliment shouldn’t go to your head. It’s a disgusting concept anyway. Would you want anyone to do that in your pocket?

11-: From a review of the Grammy Living Legend Awards, broadcast on Boxing Day 1990 on the Seven Network, by Candace Sutton, ‘armchair critic’, published in The Sun-Herald (Sydney, New South Wales, Australia) of Sunday 30^th December 1990:

Lloyd Webber wrapped up the evening by thanking Hal Prince and Trevor Nunn, as well he might, and an entire audience of Hollywood celebrities went off to celebrate while pissing in each other’s pockets.

12-: From the column Stay in touch, by Philip Clark, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Tuesday 26^th March 1991:

Cleary move to Parramatta outlawed
With pressure building on him to vacate his seat and stand in Parramatta, the State Member for Coogee, Michael Cleary, decided yesterday to enlist the help of the person he obviously considers the kingmaker in ALP politics, 2UE’s John Laws.
Listeners may have had difficulty in hearing what was being said for the background thunder of what could only be robustly described as mutual peeing in pockets.

13-: From a review of Fred Hollows. An Autobiography (Melbourne: John Kerr, 1991), by Fred Hollows ³ and Peter Corris—review by Jack Waterford, published in The Canberra Times (Canberra, Australian Capital Territory, Australia) of Saturday 14^th September 1991:

When brother ophthalmologists (not all distinguished during his career for unstinting affection to him) gathered earlier this year to honour his contribution to ophthalmology, their profession, and to public health, he embarrassedly told them that they were only pissing in his pocket because he was dying.

³ Frederick Hollows (1929-1993) was a New Zealand–Australian ophthalmologist.

14-: From Keating sits out reconciliation waltz, by Alan Ramsay, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Saturday 21^st September 1991:

Bob Hawke was Graham Richardson’s guest on Sydney’s 2KY, the radio station owned by the NSW Trades Hall. […]
[…]
Richardson: “Good morning, Bob.”
Hawke: “Gidday, Graham. How are you?”
“I’m pretty well, actually. I know I missed [a] Cabinet [meeting in Canberra] yesterday. I assume you were able to get along without me, were you?” — “Just scraped through, mate.”
“Just scraped through? Didn’t do anything to me, I hope, while I was absent?” — “I’m saving it for you, son.”
And on and on, very matey, for the best part of an hour, each peeing in the other’s pocket at a furious rate, their own Ministry of Mutual Love in stereophonic sound.

15-: From Gossip about you (don’t) know who, by Tony Squires, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Wednesday 18^th December 1991—Action was the Young Libs’ magazine:

Action’s racy gossip column, Stiletto (whatever that means), had an item which the YLs thought was right up our alley.
“The Young Liberal State president [Trent Zimmerman] is still recovering from a letter he recently received from a regional president and former State MP,” Stiletto whispers. “The letter asked him to ‘organise some young wenches and bucks’ for a new branch. The State president was assured in the letter that it was not an attempt by the regional president to ‘piss in [his] pocket’. The regional president has obviously developed a very distinctive style since leaving the hurly-burly of State politics.”

16-: From The hard word, an article about Australian book reviewing, by Jane Freeman, published in The Sunday Age (Melbourne, Victoria, Australia) of Sunday 3^rd May 1992—Helen Garner (née Ford – born 1942) is an Australian novelist, short-story writer, screenwriter and journalist:

Helen Garner says it is not just the measly pay that deters writers from reviewing (‘The Age’ pays $150 per review, ‘The Australian’ pays a minimum of $175 per review and ‘The Sunday Age’ $200 for reviews up to 1000 words).
She believes too many Australian writers know each other and are reluctant to be accused of “pissing in each other’s pockets” or being bitchily critical.

17-: From an account of Melbourne’s Writers’ Festival, by the Australian novelist, non-fiction and short-story writer Robert Drewe (born 1943), published in The Age (Melbourne, Victoria, Australia) of Saturday 19^th September 1992:

As for the Writers’ Festival proper, if that’s the right word, well, I don’t want to piss in anyone’s pocket, but I thought it was excellent.