Well, on the first level after completeing it, go to free play. Then when you are in the mission, make sure to check every door. In one door that requires a person to open it by doing the panel thing there will be a hot tub, stormtroopers bathing, and a mini-kit(I think it has a minikit. I forgot.) Then after you complete the mission it will not tell you on the UNLOCKED CHARACTERS screen but you will have unlocked a Stormtrooper with nothing but a blue bathing suit on.