One Piece Chapter 1.2, page 16: Romance Dawn (Version 2)

Suddenly, the grandfather punches young Luffy hard on the head, yelling, 'DON'T UNDERESTIMATE THE SEA-!!! THE SEA'S DIFFERENT FROM A RIVER OR A LAKE!!! IT'S A BEAST!!!! IF A SHIP GOES DOWN IN THE MIDDLE OF THE SEA, EVEN I'LL DIE!!!' Luffy rubs his head, crying, 'YOU VIOLENT OLD MAN!! How could you have done that!?' The grandfather retorts, 'A MAN WHIMPERING OVER SUCH A SMALL THING...' Luffy kicks him back: 'YOU STARTED IT!!!' The grandfather roars, 'HOW DARE YOU KICK YOUR GRANDPA!!!' The flashback ends, and Luffy smiles warmly at the memory: 'I see. You're a hammer, huh.' Anne replies, 'Forever, too.'