One Piece Chapter 2, page 16-17: THEY CALL HIM "STRAW HAT LUFFY"

Koby, remembering Luffy's words about fighting for his dreams, gathers his courage. He sweats and trembles but screams at the top of his lungs, "LADY ALVIDA IS......THE UGLIEST OLD HAG OF ALL!!!" Luffy bursts into hysterical laughter, "HA HA HA HA HA HA!" while Alvida's crew gasps in horror. Alvida is enraged, raising her mace as she screams, "YOU LITTLE--!!!" Koby stands his ground, shouting, "I SAID IT AND I WON'T TAKE IT BACK! NO MORE CRINGING FOR ME!! FROM NOW ON, I'LL FIGHT FOR MY DREAMS!!

Alvida swings her spiked iron mace with full force, screaming, "YOU'RE BOTH GOING TO DIE!!" Koby cries out, "L-LUFFY...!!" but Luffy steps in front of him, smiling, "GOOD FOR YOU, KOBY!! IT MAKES NO DIFFERENCE TO ME..." The mace strikes Luffy directly on the head with a heavy "WHAM!!" impact. However, Luffy remains completely unharmed, smiling widely as he says, "THAT DIDN'T HURT! 'CAUSE I'M MADE OF RUBBER!" Alvida is shocked, stammering, "IMPOSSIBLE! NO ONE SURVIVES THE IRON MACE!!