Jeff walks into a bar and sees his friend Paul slumped over the bar. He walks over and asks Paul what's wrong.
"Well," replies Paul, "You know that beautiful girl at work that I wanted to ask out, but I got an erection every time I saw her?"
"Yes," replies Jeff with a laugh.
"Well," says Paul, straightening up, "I finally plucked up the courage to ask her out, and she agreed."
"That's great!" says Jeff, "When are you going out?"
"I went to meet her this evening," continues Paul, "but I was worried I'd get an erection again. So I got some duct tape and taped my penis to my leg, so if I did, it wouldn't show."
"Sensible" says Jeff.
"So I get to her door," says Paul, "and I rang her doorbell. She answered it in the sheerest, tiniest dress you ever saw."
"And what happened then?"
"I kicked her in the face."
This reminds me of another joke I heard recently (via Natalie):
A Jew with an erection walks into a wall. What happens? — He breaks his nose.