WHAT IS IT AND WHY?

Probably "sit on it" actually I don't remember it being used until the episode "Fonzie moves in." The term "nerd" I remember from "crusin" it was used at the end by Bag. The term" aaaay "was used almost from the beginning, but I can't recall which episide> (Henry Winkler said he came up with "aaaay" in the 1992 reunion show)