A story related to me by a receptionist:

A particularly pesky salesman was bothering her with magic tricks and things of that sort while waiting for the person he had come to see. Getting a little perturbed by my friends apparent reluctance to succumb to his obvious charms and her seeming insistence on doing real work he pressed harder and said, "This is going to blow your mind!" My friend replied, "This is going to blow your mind. Your fly is open." The salesman immediately fumbled for his fly, which *was open, and tried to zip it up. His shirt was poking out through the fly and got caught in the zipper. He never did quite recover and he never bothered my friend again.