Blondes and Hailstone Damage

A blonde was driving home after a game, and got caught in a really bad
hailstorm. Her car was covered with dents, so the next day she took it
to a repair shop. The shop owner saw that she was a blonde, so he
decided to have some fun. He told her just to go home and blow into
the exhaust pipe really hard, and all the dents would pop out. 

So, the blonde went home, got down on her hands and knees and started
blowing into the exhaust pipe. Nothing happened. She blew a little
harder, and still nothing happened. Her roommate, another blonde, came
home and said, "What are you doing?" The first blonde told her how the
repairman had instructed her to blow into the exhaust pipe in order to
get all the dents to pop out. 

Her blonde roommate rolled her eyes and said, "Uh, like hello! You need
to wind up the windows first!"