The dress that launched 1000 ships.

Dress of Dischord: This dress is rumored to have been worn by Helen of Troy herself on the day she was abducted and appears in most ways to be a normal dress. The effects of this magical dress of unknown origin remain unfelt until someone makes mention of its color, at which point chaos is likely to ensue. There is a 50% chance that the dress will either appear black and blue, or white and gold to anyone viewing it, and will thereafter spark heated conflict between the factions of either color. These two groups immediately take on a hostile disposition toward each other and will attack -- either verbally or physically -- anyone they know to be a part of the opposing faction. There is no saving throw to resist this effect, and the blind are unaffected.