One Piece Chapter 5, page 17: CHAPTER 5: THE KING OF THE PIRATES AND THE MASTER SWORDSMAN

Luffy's rubber body stretches backward under the impact of the bullets, and he proudly yells, "BULLETS CAN'T HURT ME!!" With a powerful snap, his body bounces the bullets right back at the execution squad. The Marines scream, "LOOK OUT!!!" as the bullets fly back, knocking them off their feet. Luffy bursts into loud laughter: "HA HA HA HA HA!!!"