The Chinese answer

An American tourist goes on a trip to China. While in China, he is very sexually promiscuous and does not use a condom.
A week after arriving back home in the States, he awakes one morning to find his penis covered with bright green and purple spots.
Horrified, he immediately goes to see his doctor.
The doctor, never having seen anything like this before, orders some tests and tells the man to return in two days for the results.
The man returns a couple of days later and the doctor says,

"I've got bad news for you. You've contracted Mongolian VD. It's very rare and almost unheard of here. We know very little about it."

The man looks a little perplexed and says,

"Well, give me a shot or something and fix me up, doc." The doctor answers,

"I'm sorry, there's no known cure. We're going to have to amputate your penis."

The man screams in horror,

"Absolutely not! I want a second opinion!" The doctor replies,

"Well, it's your choice. Go ahead if you want, but surgery is your only choice."

The next day, the man seeks out a Chinese doctor, figuring that he'll know more about the disease.
The Chinese doctor examines his penis and proclaims,

"Ah yes, Mongolian VD. Very rare disease."

The guys says to the doctor,

"Yeah, yeah, I already know that, but what can you do? My American doctor wants to operate and amputate my penis!"

The Chinese doctor shakes his head and laughs,

"Stupid American doctor! American doctor, always want to operate. Make more money, that way. No need to operate!"

Oh thank God!" the man replies.

"Yes!" says the Chinese doctor, "You no worry! Wait two weeks. Dick fall off by itself!"