It's Donald Trump vs. Comedian Bill Maher.

It started when Maher appeared on The Tonight Show and really delivered a low-blow insult at Trump.  
Maher said, “Perhaps, Donald Trump had been the spawn of his mother having sex with an orangutan. Because, the color of his hair, and the color of an orange orangutan is the only two things in nature of the same color. But, unless he comes up with proof, I’m willing to offer $5 million to Donald Trump that he can donate to a charity of his choice.”

Trump promptly sent a copy of his birth certificate to Maher. It lists Fred Trump as his father, not an orangutan.

Trump told Fox News channel's Sean Hannity he's seriously thinks Maher owes him $5 million.

Trump said, “We essentially sent him a bill, a legal representation of $5 million, so he has to pay. I don't know if he has $5 million, maybe he doesn't.”

Hannity replied, “And if he doesn't pay? “

Trump answered, “Then I’ll sue him.”