This is an old joke, but I thought up a different ending.
A genie tells a man that he gets 3 wishes, but there are two catches: There’s a million dollar limit and anything he gets, his mother-in-law gets double. He wishes for a million dollars and his mother-in-law gets two million. He wishes for 2 Ferraris and his mother-in-law gets 4. He wishes for a foot long penis.