LAN parties. I remember the first time I could connect two PC together. It was Doom, with a serial-to-serial cable. We were two players on the same fucking map. It was awesome!
Then coax cable networks with friends. We used to have two or three different networks during a LAN party since you could not disconnect the coax cable to add a player without stopping the current games. The players arrived later would plug a new network just for them, and launch a game waiting the first players to finish theirs.