Somebody who you just don't respect at all. It may fit as "faggot" or "motherfucker", depends on the context.
Qu'est-ce que tu regardes là, enculé?
What the fuck are you looking at, faggot?
Bande d'enculé!!
("Motherfuckers!!" or "Bunch of motherfuckers!")
"Are you shitting me?", "are you kidding?" or "do you think I'm fucking stupid?"
A: Ils arrivent les flics!
B: Tu te fous de ma gueule?