15. Liane Cartman and Sheila Broflovski on South Park

Liane and Sheila come from two opposite ends of the mother spectrum, yet the same kind of messed-up children resulted from their craziness. Liane is promiscuous as hell and directly responsible for the little monster that is Eric Cartman. Sheila, on the other hand, is insufferably overbearing, which is just as bad. Plus, there was that time Sheila started a war between the U.S. and Canada, thus enabling Satan to walk the Earth. So there's that.