I must've been very lucky as apart from a pair of roadie-looking blokes getting seriously drunk before a delayed late night flight into KUO and starting to pull the stupid old "If this flight doesn't leave right away I'll take my bomb out" stuff (they were very quickly taken aside by some ground staff and told in very clear terms that either they STFU or have to find some alternative transportation that night - they chose to STFU) like 15+ years ago I cannot really recall anything more serious than the Y pax being allowed to use the J lavatory. This on AY, I've had all kinds of mishaps on lesser airlines

Ok, once I was flying WAW-HEL and there was only me and some other guy in J and he had clearly been hitting the lounge booze very hard. I had to endure his very drunken slur during most of the flight (he was mildly entertaining, but annoyingly repetitive in that drunken way). In the end he went back to his seat to pass out for landing, leaving the tray table next to me littered with half drank champagne glasses. The FA tried to give me a scalding about the glasses, but I just said "None of them are mine" and she clearly understood... Oh and the bloke tried to deboard with a half full glass at HEL which was quickly confiscated by the crew.