One Piece Chapter 15, page 11: Chapter 15: GONG

Boodle tries to push Luffy away, saying, "YOU YOUNG WHIPPER-SNAPPERS... YOU'RE OUTSIDERS... KOFF... NOT YOUR FIGHT! THIS IS MY BATTLE! IT'S MY TOWN AND I'LL PROTECT IT! SO DON'T INTERFERE!!!" Luffy suddenly swings his leg and kicks Boodle hard in the head with a loud "THWAK!!" sound effect.