One Piece Chapter 7, page 11: Chapter 7: Friends

Koby panics, screaming, "LUFFY!! DON'T!!" in his mind. Luffy continues talking to Ripper, "SHE WAS REALLY MEAN... AND FOR TWO YEARS, THIS GUY..." Koby snaps and punches Luffy right in the face with a massive "WHACK" sound effect, screaming, "SHUT UP!!!" Luffy is sent flying back.