A 'piss up' is British slang for a drinking session, so if you couldn't organise a piss up in a brewery, you really suck at organising things.
"Im getting married in a few months but I'm going to leave it to Steve to organise the reception"

"Fuck that! Steve couldn't organise a piss up in a brewery... I'll do it"
by L-Shizzle November 16, 2007
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When someone is so incompetent that they quite literally couldn't manage a piss up in a brewery
Person 1: "Ere, look at 'im ovver yonder"
Person 2: "does tha mean malc?"
Person 1: "Ay, that's 'im"
Person 2 "Ay, dunt trust 'im, 'e couldn't manage a piss up in a brewery"
Person 1: "Ta, fer that advice"
by Proper Sheffield lad March 14, 2022
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