piss (oneself)
1. rude slang Literally, to urinate while wearing one's clothing. I had to go to the bathroom so bad that I I'd nearly pissed myself by the time I made it home.
2. rude slang To laugh hysterically or uncontrollably. Raj's new boyfriend is hilarious. We were pissing ourselves through the whole lunch! I was pissing myself laughing at that comedy gig last night.
ˈpiss yourself (laughing)
(British English, taboo, slang) laugh very hard: Poor Kath — she was lying on the floor and we were all pissing ourselves laughing!