One Piece Chapter 1, page 11-12: Romance Dawn

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.

Shanks rests his chin on his hand, unimpressed: "A pistol, eh? Is that so..." Luffy snaps: "Are you doubting me?!" The rest of the pirate crew rallies around Luffy, laughing and cheering: "Calm down, Luffy! Let's just have a good time! Yeah! Pirates always have a good time! The sea is vast and there's lots of islands to explore! And best of all, pirates have freedom!!" Luffy's eyes light up with wonder, but Shanks quickly intervenes, eating his food: "You guys stop filling his head with crazy ideas." Yasopp grins: "But it's true! Right!?