A not-so-common synonym for flat-brimmed cap 'flat cap', most commonly used by baseball players. Also commonly used in common urban culture. It is nicknamed a douche-hat because it is common dress of many high-school douches, douchebags, assholes and jerks.
Person 1: "You're wearing a douche hat? Lame."
Person 2: "Hypocrite, you wear them all the whoop-de-fucking time, y'know!"