> One does not seriously attack the expertise of a scientist using the undefined phrase "butt-head." But one does seriously attack the expertise of a scientist using the undefined phrases "crackpot" or "crank", which are not very far from "butt-head" So while I think the ruling was correct in that the average person would not take the insult seriously, I can see why Sagan might have taken it seriously.
The first two communicate precisely what you've described, and are a significant charge to level at a scientist.
The last is a playground insult, meaning only "I don't like you" or "I think you're mean."