Answer: Nurse
During the nuclear fallout shelter scene, Louis did everything in his power to convince Sharon to sleep with him, but despite his best efforts, Sharon firmly declined. Moreover for much of the scene, Sharon misunderstood Louis' intentions, and mistakenly believed that he was leaving to join the army, to fight for his country. This was the very reason that Sharon dressed up as a nurse, as this tied in with the moment she expressed fear that Louis would get hurt. However just as the pair finished singing their duet, "Let's Do It For Our Country", Sharon eagerly reached for the door, only to find Goose and Davey lurking behind it. In that instant, Louis' true intentions dawned on Sharon, who, mortified and disgusted in equal measure, made a hasty exit.