noun: a condition, in which a person or animal spontaneously lurches into spasmodic movements consistent with a baby calf which appears to be kicking with its hind legs at a swarm of flies which aren't there; vocalization that is sharp and loud accompanies this action. The duration of this condition is seconds to minutes.
One teacher: "How are your kids today?"
Other teacher answers: "Shit, man, they've got the screaming yips. I'm about to lose my shit!"
First teacher, "Holy Jesus on a Stick, I have them next period!"
noun: in sports, a form of punishment in which the punished must run around a track. The last person in the line sprints to the front, and then jogs; the newest caboose must then sprint, etc. etc. Activity continues until a) someone pukes; b) someone collapses, or c) until the coach is satisfied.
If I have to run any more fartlets, I'm gonna lose my shit.