a hat very commonly worn in america during the 1920s. The hat then went out of fashion although some people still wear them today. Anyone seen wearing a trilby in modern times can official be labelled a twat.
1920's Joe: "How do you like my new trilby?"
1920's Harry: "That's a mighty fine looking hat"
2010 Joe: "Hey man check out my new trilby"
2010 Harry: "Dude you're such a twat"