@ the Pinakothek der Moderne - Munich
Young Lady speaks to guard (not invisible but not visible either):
Young Lady: How old do you think I am young man?
Guard: Hmm... fifty. How old do you think you are?
Young Lady: Twenty-two! I can show you my birth certificate.
Guard: I'm afraid you're going to have to show more than your birth certificate to convince a man of that.
(borrowed from "The trouble with Harry" - 1955)