Where a group of boys (the lads) go on holiday together where they get up to debaucheries most notably cheating on their girlfriends/wives for fun abroad.
*To bestmate* "Liam is going on a lads holiday next week I don't think I can cope"
Them: "nah babe its alright I'm sure he won't cheat"
Her: "no but that's what all lads do on a lads holiday"