This one is a bit lengthy, but good...
A professional tuba player goes to his doctor, complaining about constant headaches. After a series of tests, the doc puts on his "Its serious" face and explains: "See here, you are a tuba player. Most of your professional life you have been sitting down, in a cramped position, with your instrument between your legs. Thus, your, em, balls have been squeezed, and this has caused your headaches. Try sitting differently, and come back in a week."
The tuba player tries to sit differently in orchestra and gets horrible back pains added to the headaches. So he goes back to the doc and tells him about it. The doc puts on his "it's even more serious than I thought" face and says, "Ok, so your headaches have become chronic. There is no other way out of it - we will have to remove your balls entirely."
"No other way, doc?" -
"No other way, or you'll eventually go mad from your headaches." -
"Well, then..."
After the operation, the tuba player really has no headaches any more. It feels like a new life. And so he celebrates this new life by transforming himself. No mor grubby sweaters and jeans for him - he has to have a smart suit and all the trimmings. So he goes into the best men's fashion outlet in town and asks for a suit. The salesman tells him, "I've got just the thing for you," and returns with a light blue suit which fits perfectly. "How did you know light blue is my favourite colour?" - "Oh, I can estimate people's tastes pretty accurately, not only sizes... it fits, doesn't it?" - "Fits perfectly. I think I'l have a shirt to go with the suit as well." - "Certainly, sir. This one?" - "Wonderful, that dark blue shirt... and again, fits perfectly. Now for some new underwear as well." - "Of course. Here's the fitting vest for you. For the underpants I'll have to go back - I've only got size 5 here, and you need size 7." - "But I've always worn size 5..." - "Too small for you. You're a size 7. Otherwise, your balls will get squeezed, and you'll have constant headaches."