Someone who doesn't have a mental illness but acts completely fucking retarded.
Friend: *Jumps out a bus window*
Other friend: Ur fucking sped mate.
Literally short for Special Education Kid. This word doesn't mean that you necessarily require additional academic help, but that you are acting in an extremely stupid fashion.
Why did you take a shit in the urinal? You're such a sped.
Something I am, slow in the brain, mentally, when is comes to something obvious
Person 1: Your girlfriend is sped dude
Person 2: I know bro