A mishap generally involving the mass consumption of alcohol and a misdirection of urine to an area other than the toilet. This usually occurs as the result of an alcoholic stupor.
Can also apply to any other misadventure in some way linked to piss.
Man, Mark was so wasted at his birthday party last weekend that he woke up in the middle of the night and peed all over his computer. It was quite the pisshap.