A term given to one that has trouble dancing or keeping a Rhythm. Also given to those who cannot do anything at a certain pace or beat. Generally considered an insult among drummers and dancers.
Girl: -stumbles during dance routine-
Boy: Why'd you stumble on such an easy thing?
Girl: -shrugs- I guess i'm Rythmically Retarded.
Drummer 1: Dude, who is that Rythmically Retarded drummer over there?
Drummer 2: Oh, he's a n00b.