Jeff walks into a bar and sees his friend Paul slumped over a table in the corner. He walks over and asks him what's wrong.
"Well," replies Paul, "you know that girl I wanted to ask out, but I got an erection every time I saw her?"
"Yeah," 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."
I can explain it to you but I can't understand it for you.