Pirate Hat

The Pirate sells the outfit, and he does not wander in by himself. You have to beat a Pirate Invasion first, which needs Hardmode and either a raid that rolls on its own or a Pirate Map used to call one down. Give him a house afterward and he settles in.

His shelf does not rotate. The hat, shirt and pants stay in stock from then on, with no season or moon phase to plan around, so this is one costume you can safely put off until the coin is spare.

The three pieces drop into the social slots and change nothing but your silhouette. The hat alone suits any gun build, and the full set is the obvious dress code for a ship base or for anyone running a Pirate Staff.