The Infocom game Leather Goddesses of Phobos actually
required you to go to the toilet at the start (which one you used allowed the game to determine your sex with the sex of various in-game characters being amended accordingly)
Being a text-only adventure it wasn't a revealing experience though.
Not going to the toilet (that is, not making use of one) was also an option but it just resulted in a messy and abrupt game over when your self-control gave out.
