[GambleAB]

You are playing three handed. Why are you even in the game if you are considering showing the other player your hand? Besides, if the other guy has any clue whatsoever what is going on, he'd see you two softplaying each other and showing your hands, so he would probably pick up and find a game with less collusion going on.
Anyway, the "polite" thing to do is to shove (without showing your hand). If you are considering showing the guy your hand, you should prob pick up after you drag the pot, as the game prob isn't +EV for you and you'd prob feel more comfortable hanging out with your new friend.