Green Cap

The Green Cap is a vanity item equipped in the social helmet slot.

The Green Cap is a drop from killing the guide named 'Andrew'. (Names are chosen at random from a list when the Guide spawns.)

Trivia
The Green Cap drops only from a Guide with the name 'Andrew'. It's a reference to the lead programmer of Terraria, Andrew Spinks. His sprite comprises of a player with the aforementioned cap.