One Piece Chapter 2, page 7: THEY CALL HIM "STRAW HAT LUFFY"

The dust clears, revealing the three pirates knocked out on the ground. Alvida looms over them with her iron mace, demanding, "YOU LAZY SWABBIES! WHO'S THE FAIREST THROUGHOUT ALL THE SEAS?" The pirates quickly grovel, stammering, "LADY ALVIDA! YOU ARE... OF COURSE!" Alvida snaps, "DON'T PLAY DUMB WITH ME! I COULD HEAR YOU TALKING ALL THE WAY FROM THE SHIP! WHICH ONE OF YOU HAD SUCH A 'GREAT NAP'!?" She glares at them, asking, "AND YOU DARE TO DEFY ME?" One pirate stammers, "W-WHAT!? NEVER! NOT IN A MILLION--" Suddenly, Luffy's voice echoes from nearby, cheerfully repeating, "THAT WAS A GREAT NAP!!!" Alvida and her crew gasp in surprise.