"Jumping Blonde" joke

A
blonde, brunette and a redhead run to the top of a burning
building. Below, a few firefighters are holding a blanket
telling the redhead to jump.
When the redhead jumps the firefighters snatch the
blanket away and she hits the concrete.
When the firefighters ask the brunette to jump she
jumps and again they pull the blanket away.
When the firefighters ask the blonde to jump she
replies, "I don't trust you, so just put the
blanket down and back away."