Well, I think they're an example of an exocentric compound. Neither the "boat" nor the "face" is insulting, but there's an implication of ugliness. ("boatface"

Well, I think they're an example of an exocentric compound. Neither the "boat" nor the "face" is insulting, but there's an implication of ugliness. ("boatface" implies "boat-faced scoundrel" or equivalent).