For a tattoo, you want to be awfully careful!
I would suggest: "In the game of life, there are no winners--just people who think they've won."
But I don't understand the meaning. Does your friend mean that the people who think they've won are foolish? Or that they are wise?
Does "There haven't been any winners in the game called life yet" mean that are never any winners, life is not a game and can't be lost or won? Or does it mean that someday there _will_ be a winner?
I would be very, very, very careful. Whatever wording your friend comes up with, he or she should be sure that people who read it understand what he is saying.