(This was on an IBM Aptiva with Windows 3.1. You could set it in sleep mode just by pressing the power button. This was amazing for its time (1995) I think - I didn't see that feature again on any machine I had access to until a laptop in 2003 or so.)
The DB25 serial port on the A1000 (first Amiga) was different from other systems of the day. Not just the obvious gender difference, but the pinouts were different as well. I knew a couple guys who tried a A1000 <--> A500 hookup, and blew one or both computers.
Game netcode got better, and so did network infrastructure, so in time this ban got lifted. Though part of me thinks that they couldn't actually enforce this ban without punishing half the school. Doom was that popular... at least until Quake came out.
LAN parties have been around a lot longer than that. Friend of mine used to play DOOM deathmatch with his housemates at uni back in the 90s.
One of them was really good at designing levels but really terrible at the game, so he'd always hide the BFG somewhere that obviously only he'd know about so that he could go and grab it and then wipe out the other players relatively easily.
The others quickly got wise to this and, of course, DOOM was really easy to mod. For example, changing sound effects was simple: you could just overwrite them with different sound files on disk, I believe. So what they did is replace the sound that played when somebody picked up the BFG with the full length theme from The A-Team. DOOM didn't have the most sophisticated sound engine by today's standards, but it did have directionality, and sounds did get quieter the further away the source, and louder the nearer it was.
So the upshot was you had early warning that the guy had picked up the BFG and could either avoid or sneak up on him as appropriate. Apparently this used to really annoy him.