It's a physical reaction that a person has when they get over stimulated or excited when typing, often when someone is in the act of Instant Messaging. It causes the typer to make several mistakes and become flustered, eventually just feeling exhausted and unable to continue typing.
Jen: What happened when you were talking to Craig in the chat room?
Cheri: I got so excited that I completely keygasmed and finally logged off.
Ruler of Lake Titicaca. Rumored to have a bunghole that gets very angry if it does not receive toilet paper. Cornholio the Great is often seen walking around with his shirt over his head and his hands in the air, chanting songs about his power, and his bunghole.
"I am Cornholio! You do not want to face the wrath of my bunghole, for I need TP!"
Butthead: Shut up, Beavis! (uh huh huh huh)
Beavis: Um, okay. (heh heh heh heh).