When you hold down the shift key to use "!" (or any other thing you need the shif to use)multiple times and you "slip" on the last one.
Mark: Are you okay man?
Kyle: HELLZ YEAH I AM!!!1
Mark: Shift slip?
Kyle: yeah...
When you try to press the ! key on your computer a billion times, and it looks something like this: !!!!!!1111
Oh Man!!!!!11 i just sent message on facebook and accidentally shift-slipped, they're all goin' to think I'm a noob!!!!!111