One of my favorite insults actually isn't from a movie, but from a cartoon. In the Bugs Bunny cartoon "Bewitched Bunny", Bugs discovers a witch luring two children into her house. The children turn out to be Hansel and Gretel. Bugs warns them that the witch is going to eat them and they flee the house, but on the way out they stop in front of the witch, kick up their heels, and yell, "Ach! Your mother rides a vacuum cleaner!"
Every time I see that cartoon I just fall out at that line. I'm giggling now in fact.
This is the cartoon where, at the end, Bugs tosses a bomb containing magic powder at the witch, turning her into a seductive female bunny. As the two of them walk off arm in arm, Bugs smiles at the camera and says, "Ah, but aren't they really all witches?" That line has provoked complaints from viewers in the past, one of whom filed a complaint with the Canadian Broadcast Standards Council. The record of disposition of the complaint can be read at http://www.cbsc.ca/english/decision/980203a.htm. That's worth a chuckle itself.