Watch Episode of Nami. If you like that, pick up the series.
If you want something you can LEGALLY watch, watch one of these movies: Strong World, Film Z, or Film Gold. They have some spoilers, but all three are great introductions of what One Piece is all about. It's how many people got into the series in Japan. They're in the style of the Dragon Ball Z films Battle of Gods and Resurrection F' in production quality. All three films have their own beginning, middle, and end plotlines and they're genuinely great.