One Piece Chapter 1.1, page 24: Romance Dawn (Version 1)

Luffy winds up his arm and throws a powerful punch. His arm incredibly stretches like rubber across the street, striking both pirates simultaneously with a massive impact. The pirates are sent flying backward, screaming, "BUBEH!!!". Shiruku watches in absolute shock, her eyes wide and her mouth agape, uttering, "!!!?" as Luffy's stretched arm snaps back to its normal length.