ArcheAge? It's doable according to a translated post on the ArcheAge Source fan forum. The game's PvP implementation features a familiar "red" flagging system for outlaw players. Killing (or stealing from) your fellow players will result in bad karma. When your meter gets to 3,000, you're a red, and you can do things like form a pirate expedition force (we have no idea either, but it sounds cool).
Pirate factions can only be joined by other pirate players, and you won't be able to interact with NPCs on the game's starter continents (you'll also aggro the guards). Fear not, though, as pirate players do have access to their own island filled with friendly NPCs and quests. Click past the cut to see some booty-plundering gameplay courtesy of a twelve-minute video.
[Thanks to Dengar for the tip!]