Online and at casinos it is true that the agressor is the first to show, then others show if they win, and much if they don't.

But at my home game, we rarely have this problem. But on the occations it comes up. We just go in order of how it was delt. BB, CO and Button all go to showdown. BB shows 1st, CO either shows or mucks, and Button shows/mucks last.

If it is a problem, there should be a rule. But I don't think it matters as long as it's fair and aplies to everyone.