Growing bored with playing Gorilla.bas, I wrote a program that let out a several second long, <100hz tone, a "Fart" if you will, and then printed "oh, sorry, I couldn't contain myself!".
I backed up autoexec.bat as autoexec.old, wrote a new autoexec that ran my program, deleted it, and then restored the original autoexec.bat to cover its tracks.
We weren't present when it did its thing, but the next day I was informed that if it happened again, I'd lose access, and that was it. No "hacking" accusations or anything.
I also remembered another detail: Apparently the same fellow, who had a reputation for smart but also extremely difficult to deal with (I wouldn't know, never met them) also had their fingers in one of the first dialup Internet services in the area, cleverly named DNIS (Desert Network Internet Service, I think? It was basically an Internet connected Linux shell if I recall) but everyone locally called it PNIS. Poor guy.