A man went to the doctor and said, "Doctor, I've got a problem, but if you're going to treat it, first you've got to promise not to laugh.
"Of course I won't laugh," the doctor said.  "I'm a professional.  In over twenty years I've never laughed at a patient."
"Okay then," the man said, and proceeded to drop his trousers, revealing the tiniest penis the doctor has ever seen.
Unable to control himself, the doctor fell laughing to the floor.  Some minutes later he was able to struggle to his feet and regain his composure.  "I'm so sorry," he said. "I don't know what came over me. On my honor as a doctor and a gentleman, I promise it won't happen again. Now what seems to be the problem?"
"It's swollen."