This Bruno Mars photo contains
fedora, felt hat, homburg, stetson, trilby, boater, leghorn, panama, panama hat, sailor, skimmer, straw hat, dress hat, high hat, opera hat, silk hat, stovepipe, top hat, topper, and beaver.
There might also be
pith hat, pith helmet, sun helmet, topee, topi, porkpie, porkpie hat, and campaign hat.