Magic: The Gathering Thread XIV: Instant Annoying, Just Add Hexproof

[IthilanorStPete]

The stump-the-judge question is some variation on the following:
It's a multiplayer game with 3 remaining players. Player A has a Door to Nothingness, Player B has a Leyline of Sanctity, and Player C has nothing important.

Player A taps lands for 2 mana of each color, and then announces that he is using the Door's ability. Before he announces the target, Player C concedes. Can Player A avoid targetting himself with the Door to Nothingness?

Huh, that's an interesting dagger. I think Player A's out of luck, but I'm not familiar enough with the intricacies of multiplayer rules to be sure.