The repairman, noticing that the woman is a blonde, decides to have a wee bit of fun, so he tells her all she has to do is take the car home and blow in the tailpipe until the dent pops itself out.
So she does. After 15 minutes, the blonde's blonde friend comes over and asks what she is doing.
"I'm trying to pop out this dent, but it's not really working."
"Duh," laughs her friend.
Spoiler: