A clip from the Simpsons episode "Milhouse doesn't live here anymore" with Groundskeeper Willie discussing natural enemies. (...)
Willie: Brothers and sisters are natural born enemies! Like Englishmen and Scots! Or Welshmen and Scots! Or Japanese and Scots! Or Scots and other Scots! Damned Scots! They ruined Scotland...
Skinner: You Scots sure are a contentious people.
Willie: You just made an enemy for life!