Please settle this: Player A calls Player B’s hand. Player B shows the winning hand. Player A just folds his hand without showing it. Does Player B have a right to see Player A’s cards?
In this case, where B is both the last aggressor and the apparent winner of the hand, the only reason for him to want to see A's hand is if he suspects collusion. He can ask the dealer and/or floorman to show A's hand, but the floorman may decline (depending on house policy). It is universally considered rude to make such a request without good reason.
If the floorman does show A's hand, it is live and will win the pot if it is better than B's, so he asks to see it at his own risk (in different situations the dealer will kill a hand before showing it).
If Player A called Player B then Player B was last aggressor.
Last aggressor (Player B) is obligated to show first.
In some rooms Player A is NOT required to show. In some rooms anyone in the the hand can request a hand be shown. It would not make sense to have an order to show if all players had to automatically show anyway.
If you have the nuts from any position it is proper etiquette to show immediately. If you wait your turn that is a form of a slow roll.
If Player A showed first (out of order) is Player B required to show is more interesting. In most rooms Player B would be required to show. But Player A could have just waited for Player B to show first if s/he wanted to see.