In British slang:
– the adjective pissed, frequently used in similes such as pissed as a newt, means drunk, intoxicated;
– the noun piss-up denotes a heavy drinking bout;
– the phrase couldn’t organise a piss-up in a brewery and variants mean is, or are, or am, incapable of organising the simplest event, task, etc.

—Synonyms:
– to be unable to run a whelk stall;
– couldn’t lead a flock of homing pigeons.

The earliest instance of the phrase couldn’t organise a piss-up in a brewery and variants in the Oxford English Dictionary (3^rd edition, 2006) dates from 1982; the earliest that I have found is from The Observer (London) of 9^th November 1980; in an article titled Halewood heads for a showdown, Michael Nally reported that, among the “intemperate explanations for the crisis at the Ford car plants at Halewood on Merseyside [that] flow thick and fast in local bars at lunchtime”, one from a worker was:

“They couldn’t run a piss-up in a brewery. They can’t manage the machines, let alone the men. If Henry Ford could see them at it, he’d have a fit, poor lad.”

Andrew Moncur noted the following in his column Diary, published in The Guardian (London) of 14^th November 1989:

Media News (Part III). A word for staff at BBC’s London radio station, GLR, from Matthew Bannister, managing editor: b******s. I’m sorry, but it’s there, in black and white, in his memo to producers and presenters on the subject of bad language. He has been moved to intervene after a series of unfortunate slips-of-the-tongue on air. “Without wishing to sound pompous, may I suggest the following translations,” he writes. “Stark bollock naked” (Janice Long) = stark naked; “I expect you’re very pissed off” (May Costello) = I bet you’re very depressed; “You couldn’t organise a piss-up in a brewery” (James Cameron) = You couldn’t organise a party in a brewery/You must be very disorganised. Mr Bannister’s note explains that use of rude words is indefensible. He adds, yet more helpfully: “So, let’s not hear any more of this bollocks on the radio, OK?” There, now I’ve said it. Sorry about that.

The phrase has come to be used in Australian English; on 7^th December 1994, The Sydney Morning Herald (Sydney, New South Wales) published this letter from one Stephen Walsh (Toohey’s is an Australian brewery):

I’m worried by the decision of Toohey’s boss Jim O’Mahony’s to cancel his company’s Christmas party (Herald, November 29). If he, of all people, can’t organise a piss-up in a brewery, who can?

In his column Pendennis: The Observer diary. Because who said life was fair…, published in The Observer (London) of 17^th December 1995, Oliver Marre wrote the following under the title They can organise a piss-up in a brewery:

The week in Central London has, alas, been almost entirely spent circumnavigating gutters filled with twitching souls testing our percipient Health Secretary’s new booze guidelines to self-destruction. Young Dorrell¹ certainly has an odd sense of timing – and one rendered all the odder by the experience of his deputy, John Bowis², only a few days before.
Bowis was a guest at that bounteously vinous party in the Reform Club where John Major³’s house biographer Bruce Anderson had a wine glass smashed in his face by a fellow hack’s wife. Had the Minister tarried a few minutes longer, he would have seen Bruce with blood dripping from his face (and a Pendennis scout similarly bleeding after a valiant attempt at peacemaking). The argument was triggered by another woman guest collapsing on the floor, who then had to be rushed to hospital. She fell almost at Bowis’s feet: whereupon he memorably observed that being a Health Minister did not qualify him to administer first aid, and left.

¹ Stephen Dorrell (born 1952), Conservative politician
² John Bowis (born 1945), Conservative politician
³ John Major (born 1943), Conservative politician, Prime Minister 1990-1997