Say for some inexplicable reasons, your girlfriend and your mother switch bodies. By that, I mean both of their minds, including personalities and full awareness of everything, is in the opposite body. You learn that if you do not bang one of them, all three of you are going to die. Once you finish, everything will return to normal, but memories of the event would stay with all of you forever. Who would you bang? Your girlfriend's mind in your mother's body, or your mother's mind in your girlfriend's body?
For girls, it's the same, but with your boyfriend and father.
PS: If you're homosexual, both participants are whatever gender you're attracted to, I.E. your boyfriend and your father.
[u]If you're not in a relationship, it's your crush/dreamy one.[/u]