why i ougthtta...!

a threat often accompanied by a n arm gesture of backhanding someone in the face; it means I ought to slap you in the face (or do something worse); exactly WHAT the speaker ought to do is implied almost as if it is a fill-in-the-blank statement where the blank is filled in with something very bad. It isn't a question. (The "why" part of the phrase isn't asking why, it's telling the listener that something bad should happen to him because of what he just said or did wrong.)