One Piece Chapter 1, page 11: Romance Dawn

Hahahahaha You?! A pirate?! Impossible!!" He teases the boy: "Luffy, do you know why we call you 'Anchor'? Because you can't swim—you just sink!! What good is a pirate who can't swim?" Luffy argues back: "But if I don't fall overboard, then it doesn't matter if I'm an anchor!! And I'm a strong fighter! I've been training! My punch is as powerful as a pistol!" He throws a punch into the air to demonstrate.