Not "all there in the head"; possibly lacking intelligence or common sense. The wall-eyed background character in "My Little Pony: Friendship is Magic", Derpy Hooves, is named after this.
Hey, look at that guy sticking his aluminum foil-wrapped dick into an electrical outlet. That's derpy if I've ever seen it.
Derpy is best pony.
Derpy is best pony.
by datSato January 01, 2012
by datSato September 06, 2009
In the context of Speedrunning, this is often said in a joking or sarcastic manner when a trick or other act takes more than one attempt.
Speedrunner: *Fails to make a jump four times, then finally succeeds in making the jump*
Speedrunner: Hey, first try!
Speedrunner: Hey, first try!
by datSato July 25, 2018