I'll start off with a few of my favourite ones:
- Peter: Excuse me, is your refrigerator running?
Because if it is, it probably runs like you - very homosexually.
Peter (after Lois tells him he's childish): "If I'm a child that means you're a pedophile, and I'll be damned if i'm going stand here and take this from a pervert."
Peter: Ok, here's another riddle. A woman has two children. A homicidal murderer tells her she can only keep one. Which one does she let him kill?
Brian: That's... that's not a riddle. That's ... that's just terrible.
Peter: Wrong, the ugly one!