Your hairline's so far back, even Rosa Parks refused to sit in the back; it went all the way there itself.
The Receding Hairline
Explanation
Explain Bear
Listen, smooth-brain. Rosa Parks is famous for refusing to go to the back of the bus. The joke says your forehead is so massive and your hair is so far back that it reached the back row before anyone else. You're balding faster than you can process this sentence. It's a roast, and you're getting cooked.