Proverbially, the thing that a particular bad organiser couldn't organise, even if by pure dumb luck he happened to find himself in the place where beer is produced.
Another government IT project's gone pear shaped, seems EDS really couldn't organise a piss-up in a brewery.
More commonly used in Australia; basically a social gathering or full-blown party intentionally to get drunk. Commonly associated with pisswrecked, pissed, wreckless, drunken, wrecked, fucked.
In the holidays, there was a massive-arse piss-up to celebrate no school. 'Twas well-sick :)