Summer Hat

The Clothier only puts this out during daylight hours, and since a recent update he will not sell it while he is standing in a graveyard. If it has vanished from his stock for no clear reason, count the Gravestones near his house: enough of them will have flipped the biome without you noticing.

It is pure vanity, so it goes over real armor and costs nothing.

A straw hat with a red band, worn by a certain rubber pirate captain. Its item id sits in a run of other reference outfits added around the same time, which reads like the whole batch went in as one joke rather than this one being a coincidence.