A blonde had a dent in her car and took it to the repair shop to have it removed. Noticing that the girl was a blonde, the mechanic, thought he'd have a little fun. He said to the girl "Go home and blow as hard as you can into the tailpipe and that dent should pop right out." The girl went home and did as she was told.
After about 15 minutes of blowing, her friend came over and asked what she was doing.
"Well, I'm blowing into the tailpipe to make the dent pop out, but it's not working" she sighed.
"Well duh, you have to roll up the windows first"