From Longman Dictionary of Contemporary Englishpiss yourself (laughing)piss yourself (laughing) spoken not politeBritish English to laugh a lot, especially when you cannot stop laughingThey were all copying my accent and pissing themselves laughing. → piss
Examples from the Corpus
piss yourself (laughing)• He felt very cold, and he had pissed himself.• We both pissed ourselves laughing afterwards, wondering what all the fuss was about.• No older girl has ever pissed herself on account of Laverne before. 