One Piece Chapter 8.3, page 18: Nami Enters

One of the large, stitched-faced pirates confronts Luffy, saying, "AM I RIGHT? BOSS! THAT MAP WAS CAPTAIN BUGGY'S TREASURE!!" He swings his sword, slashing the top of Luffy's straw hat. Luffy gasps in shock as his hat is damaged. Enraged, Luffy delivers a powerful punch that sends the pirate flying backward into his comrades, knocking them all down. Luffy catches his falling straw hat, his face turning serious and angry as he warns, "DON'T YOU DARE... MESS UP MY HAT!!"