In Australian English, the colloquial noun chewy denotes (a piece of) chewing gum, and the phrase chewy on your boot is used:
– in the context of Australian Rules football: as a call to discourage or distract a player in a rival team, especially one attempting to kick for goal;
– more widely: to deride a person or organisation deemed to be performing poorly, or to wish someone bad luck.

This phrase occurs, for example, in Team of the week, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Saturday 13^th May 2000:

KIEREN PERKINS ¹.
This is it, Kieren. This week. Just you and 1,500m of water, and two spots open on the Olympic team. We don’t reckon you can do it but, just in case, have asked the waiter to bring us two hot humble pies with lashings of crow on the side, plus a lid to dip in your direction if you do it. Good luck. Go for it. Chewy on your boot.

¹ Kieren Perkins (born 1973) is an Australian freestyle swimmer.

The earliest occurrences of the phrase chewy on your boot that I have found are as follows, in chronological order:

1-: From The Australian Language: An examination of the English language and English speech as used in Australia, from convict days to the present, with special reference to the growth of indigenous idiom and its use by Australian writers (Sydney: Currawong Publishing, 1966), by Sidney John Baker (1912-1976):

chewie, chewing gum. Whence, do one’s chewie, to become angry or irritated. Hope you have chewie on your boot! used to express a wish that a football player kicking for goal misses because there is chewing gum on his boot.

2-: From the column Ebenezer, by Peter Smark (1936-2000), published in The Age (Melbourne, Victoria, Australia) of Wednesday 11^th June 1975:

There are many reasons to be so proud [to be Australian]. Look at the cricket in England, for instance.
There was poor little Jeff Thomson, innocent, inoffensive wee mite, having a trace of trouble with his run-up.
Those rude, rough Poms actually heckled him. No, truly they did. They called out spiteful words—“Chewy On Your Boot” or similar. Well I mean. Naturally Jeffie raised his hand to brush away the tears, so hurt was he.
And now those dreadful English papers have gone and accused him of making a rude gesture.

3-: From Hawke’s two speeches draw total of 600, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Saturday 8^th November 1975:

Mr Hawke ² said […] after the 1974 election Labor had settled down to the business of government, but the Opposition had been trying to find an issue to pervert the will of the people.
“Then they found this man Khemlani ³,” he said.
[…]
Mr Hawke puzzled the crowd when he described their reaction to the Khemlani disclosure as, “You were wrong, chewy on your boot.”
He did not seem to realise he had used an Australian Rules cat-call.

² Bob Hawke (1929-2019) was the National President of the Australian Labor Party from 1973 to 1978.
³ In 1975, the government of Australia, led by Gough Whitlam (1916-2014), of the Australian Labor Party, was accused of attempting to borrow money from the Middle East by the agency of the Pakistani banker Tirath Khemlani (1920-1991) and thus bypass the standard procedures of the Australian Treasury and violate the Australian Constitution.

4-: From the following letter to the Editor, published in The Canberra Times (Canberra, Australian Capital Territory, Australia) of Wednesday 14^th June 1978:

Wanniassa High School

Sir,—As a student who will be badly affected by the non-opening of Wanniassa High School, I feel it my right to say something.
We have been told that Kambah High is not full to capacity so we must go there. […]
[…]
I live next to an empty high school, and will have to catch a bus to another suburb. I’ll bet the ACT Schools Authority won’t give us free bus travel. Then I will be made to take the left-overs from subjects offered.
Then, sometime later, we will be uprooted from Kambah and finally returned to the Wanniassa High, where I should have been in the first place! “Chewy on your boot” to the ACT Schools Authority.
(Miss) R. BEAVAN
Wanniassa.

5-: From an interview of Charlie Callender, Property Steward of the Richmond Football Club, an Australian Rules football club based in Melbourne—interview by Gerry Carman, published in The Age (Melbourne, Victoria, Australia) of Saturday 25^th September 1982:

With the panache of a “chewy on your boot” stylist, he recalls part of the club’s history which would irk any loyal Magpie ⁴. “Collingwood cleared Dan Minogue to us in 1920 and he led Richmond to a premiership in 1920-21,” Charlie says proudly.

⁴ This refers to the Collingwood Football Club, nicknamed the Magpies, an Australian Rules football club based in Melbourne.

6-: From Fans are entitled to their cheering, by Mungo MacCallum, published in The Sun-Herald (Sydney, New South Wales, Australia) of Sunday 12^th October 1986:

Partisan audiences have always been part of sport. Ask the American Davis Cup team about the Australian fans who cheered wildly every time the Americans hit a ball into the net or the Rugby League goalkickers who put up with the screams of “lolly legs” and “chewy on your boot” whenever they line up a penalty attempt.