Messing up, making a mistake, or just being a loser. Kind of like the old Homer Def. Can also be a gay sexual position.
Man, he really pulled a masten.
Masten is an wonderful, intriguing creature. He is always eating shrimp but be careful, if he eats too many he will fall into a deep hibernation for days (like a bear!).
ADDITIONAL WARNING: He can get a whole lot more retarted.
(Ho walks in room)
Masten: BITCH get me a sandwich.
Ho: Uh.. ohkay.
Masten: That's what I thought!