What Is A Piss-Up?
For the benefit of Mr Fab
The Oxford English Dictionary (well the one we have) doesn’t list piss-up. However it does say:
Piss v.t/I (vulgar) 1 to urinate. 2 (in p.p.) drunk. – n. (vulgar) urine; urination.[f. OF pisser (imit.)]
So to clarify a Piss-Up is a gathering where everyone gets very, very drunk. Simple as that 🙂