What is the Hung like a black man joke?

A White man rubs on a genie bottle and the genie comes out and says, “Man, I’ve been in this damn bottle for 300 years, whatever you want, you don’t even have to say it, just think it and it’ll happen.”
The man closes his eyes, Bam Mansion! He closes his eyes again, Bam Filled with beautiful naked women.
And then he closes his eyes a third time. Later, three men in white hoods knock on his door. He answers it, and they take him outside and hang him.
Later, the genie is at the coffee shop talking to all the other genies, and he says to his friends, “Man I don’t get it, the first wish is always the mansion, the second wish is always women, but why on earth would this man like to be hung like a N*gga?”