"I Swear, If You Existed, I'd Divorce You."

If the recipient of this insult had been a philosophy professor instead of a mere history  professor, he might have responded as follows.  "Darling, by the Existence Symmetry of Relations, if a relation R holds, then either all of its relata exist or none of them do. Now one cannot divorce a person to whom one is not married.  So you and I stand in the marital relation.  It follows that if I don't exist, then you don't either."