The first two that come to mind for me are;
From Natural Born Killers; "We don't kill nobody on our wedding day."
And, from a movie I can't remember the name of, is Betty White talking to a cop about her alligator in the lake. "If I had a dick this is where I would tell you to suck it." Coming from Betty White made it sooooo funny.
Oh and the now classic line from The Adams Family movie;
Be afraid, be very afraid.