It is a way to say owned which also implies that your action was, after a fashion, backward in mental or physical development - In other words a synonym for retarded actions that are, in fact cool!
Larry: Dude, that was awesome! OWNAMAR!
Bob: Yeah! I really owned that half pipe!
Larry: Too bad you saw your ass.
Bob: Ownamar, you saw that?
Bob: Yeah! I really owned that half pipe!
Larry: Too bad you saw your ass.
Bob: Ownamar, you saw that?
by The South African Chommies August 4, 2007