Moxie Mike
Full House
I've had this happen almost exactly the same way you described, @Jimulacrum, albeit it was in a live game. When it became apparent around 5th or 6th st by his board and betting patterns that he wasn't aware the game had shifted to Razz, I simply said 'You do know how Razz is played, right?' This was met with the predictable... '... uhhh the game is Razz?!?!' response the resulted in an immediate muck after the rest of the table confirmed it.
I raked my pot and we moved on.
As to ethics, you would have been within your rights to take advantage of the situation but there's merit in keeping the game friendly and saving a guy from going to the felt when he has absolutely no chance to win. That said, in my situation it was only appropriate to speak up since I was actively in the hand. There's an implied responsibility that if you're gambling, you understand the rules of the game you're playing.
I raked my pot and we moved on.
As to ethics, you would have been within your rights to take advantage of the situation but there's merit in keeping the game friendly and saving a guy from going to the felt when he has absolutely no chance to win. That said, in my situation it was only appropriate to speak up since I was actively in the hand. There's an implied responsibility that if you're gambling, you understand the rules of the game you're playing.