One Piece Chapter 6, page 17: Chapter 6: Number One

Luffy relentlessly pummels Captain Morgan, landing a barrage of punches right to his face with a loud "KA-WACK!" sound effect. He declares firmly, "I'M NOT GONNA DIE." Morgan is sent flying backward from the sheer force of the blows. Koby and the Marines watch in absolute disbelief, with Koby shouting, "HE'S JUST TOO STRONG!!" while the Marines cry out, "CAPTAIN MORGAN... HE'S GETTING PUMMELED!!"