I was watching One Piece when I remembered that there was a guy Sanji saved back in the Baratie arc. Then I looked up his name, and it was Gin.
I remember that when Krieg launched the poison attack, Gin gave his mask to Luffy, essentially sacrificing himself in the process.
They said he took a lethal amount of poison, yet we don't know if he died after the events. We only know that he and his crew (including Pandaman) sailed away on a ship that wasn't the ideal size, and Gin said to Luffy that he's going to meet him again.
Did he die? I'm quite far in the story, and he hasn't returned thus far. Challenging Luffy also wouldn't be a very sane idea if he knew he was going to be dead in couple of hours, and there's virtually no chance they meet again in that time.