He gives it a rub and out pops a genie. The genie says, "I will grant you three wishes, but whatever you get, I will give your ex-wife double."
[Wait! It's not the one you think.]
The guy says, "Okay, first I want a billion dollars."
"Fine," says the genie, "your ex-wife now has two billion."
"Next, I want an IQ of 200."
"Fine," says the genie, "your ex-wife now has an IQ of 400."
"Great," says the guy. "Now I want an 8-inch penis."