Pedo's Race

Alright listen up, buttercup. So, you know how pedos are nasty and like kids? And you know how in a race, the person in the back is behind? Well, the punchline is a dirty joke that uses "behind" to also mean someone's booty. The joke is also kinda playing on "coming behind" which could also mean being late to the party. BOOM. Explain bear out!