Doctor don't laugh -
The doctor said to his worried patient "Of course I won't laugh, I'm a professional. I have never laughed at a patient".
"O.k. then", said Bob, and proceeded to drop his trousers, revealing the tiniest todger the doc had ever seen. It couldn't have bigger than an AAA battery!
Unable to control himself, the doc started giggling, then fell laughing to the floor. Ten minutes later he was finally able to struggle to his feet and regain his composure.
"I am so sorry" said the Doctor. "I really am. I don't know what came over me. On my honour as a doctor and a gentleman, I can assure you it won't happen again. Now, what seems to be the problem?"
"It's swollen", replied Bob.