although done it myself a few times got to say the funniest one i have ever seen didn't involve me.....thankfully.
was at a wedding when i was in my mid-20's, big posh do in a huge marquee; later on in the evening when everyone is well oiled a bloke had fallen asleep with his head slumped on a table next to us.
Suddenly said bloke stands up, does all the motions of opening an imaginary door, lifting up an imaginary toilet seat, unzips himself and proceeds to do a piss right in the middle of the marquee in front of all present, flushes the imaginary toilet, zips himself up, sits back down and slumps back on table fast asleep.
absolute legend.