This deals with Unhinged cards, so competitive REL is useless here. Imagine that I have a Gleemax on the field. It says:
You choose all targets for all spells and abilities.
1) Somebody sitting next to me plays an Ass Whuppin' and tries to target my Gleemax. Can I choose the target for the Whuppin'?
Destroy target silver-bordered permanent in any game you can see from your seat.
2) What if we both have a Gleemax? Then what?