All levels, mini-games, and hats
Go into the options menu and enter "Roygbiv" as a player name. Select "Submit", and you will hear the foghorn sound to confirm correct code entry.
Hats
Go into the options menu and enter one of the following player names. Select "Submit", and you will hear the foghorn sound to confirm correct code entry. Go into the hat menu and the corresponding hat will be unlocked.
2 (Tom Fulp) - TomFulp
4 (Blonde hair) - Cletus
5 (Red hair) - April
7 (Jheri curl) - Superfly
8 (Pirate bandana) - Goodman
11 (Top hat) - Grrl
12 (Diamond tiara) - Abe
13 (Daisy headdress) - Princess or Betty
14 (Dick Tracy hat) - Dandy
(Rooster) - Behemoth