Usenet. One of its best features was crossposting, where you could post one message to multiple groups simultaneously. So you could say things that would infuriate all of them simultaneously and stand back and watch them get into a huge fight over nothing. Star Trek and Star Wars nerds were really easy to get fighting each other and convince that the other group was invading them.
Similarly Apple and PC nerds.
And you could make the SF groups explode in mindless rage by just saying Heinlein was either great or was a fascist.
Old chat servers where if people were connected with the right kind of modem, you could type "+++ATH0" into the chat, it would trigger Hayes commands, and ATH0 was the command to make the modem hang up. You could tell this worked when half the channel suddenly disconnected.
MUDs and MUSHes and MUCKs. These were multi-user text games you could telnet to and in the original MUD, it was something like Zork but with multiple players simultaneously. Later MUSHes, MUCKs and other variants were more social in nature, like Second Life in text, but usually with themes, like FurryMUCK. The content was mostly player-created, and you could create places and objects by coding them. So for instance, you could code a vending machine that spawned other objects. And before they fixed this, you could have them spawn other objects that could themselves spawn other objects.
So you could create objects that would spawn other objects and have them go around doing annoying things or just spawning more and more until the server crashed. (Later on, creating annoying objects that would fuck shit up became popular on Second Life and things like GMod but I'd lost interest in pure griefing for its own sake by then.)
