A girl who tells a boy into doing something bad, lies on him, and get someone to treat him like a bad guy to tarnish his reputation.
Kim: Pour milk on that boy’s hat.
Chris: Why?
Kim: (Forces Chris to pour milk on the other boy’s hat).
Chris: Sorry, Tom. Kim, you funky doghead bitch!
Tom: (Sees Chris as a bad guy, and got his friendship ruined with Chris).
A headcrab funny is defined by any time in a half life game valve decided to be funny and put a headcrab in an unfortunate spot where the player might not see it until it's too late