I would probably break up the fight. In all honesty, everyone should.
Unless if that person really annoys you, then you know you have to get involved but make it look like you're trying to break it up.
*tries to study Emergence of Bangladesh: Ancient Bengal* Matsyanyayam- When the law of punishment is kept in abeyance... okay what? *searches dictionary* oh! Ok. In abeyance, it gives rise to such disorders as is implied in the proverb of fishes i.e the larger fish swallows a small one- wait fishes eat each other!? Is that like... fishy cannibalism!?...Oh! It's 8:30! Time for dinner! *throws book on floor*