You are the third person to claim that J.B.’s answer was incorrect. To get a disinterested third opinion I asked the poker foreman at the Red Rock hotel/casino. He said that exposing cards is not allowed in a tournament or if more than two players are still in the hand. However with only two players left in a cash game hand if one of them wants to be a fool and expose his cards that would be allowed at the Red Rock. I later asked the same question at the Wynn and the answer was the same.