One Piece Chapter 1, page 10-11: Romance Dawn

Later, inside Partys Bar, the pirates raise their mugs in a rowdy toast: "To Luffy's... courage... and to our great voyage! A toast!!" The tavern is filled with laughter and shouting: "Grog! Grog! Grog! More grog!" and "Har har har har! Drink up!" Luffy, now wearing a bandage under his eye, sits at the bar next to Shanks. Luffy boasts: "It didn't hurt a bit!" Shanks immediately calls him out: "Liar! That was a foolish thing to do!" Luffy turns to him with determination: "I'm not the least bit afraid of getting hurt!! Take me with you on your next voyage!! I wanna be a pirate too!!!

Shanks bursts into loud laughter: "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.