This is regarding a texas holdem no limit home game. After the flop, player 1 and player 2 are the only remaining who bet. After the turn of the river card, player 1 goes all in. Player 2 decides to call but does not use the word "call" but says "full house" and flips his cards over. Player 2 has the highest hand. What happens in this situation?
Because Player 1 made the final raise, he should be the first to show his cards when players reach the showdown. However, according to the World Series Of Poker rules,
When a player holds a hand that is likely the winner, they should show that hand immediately to speed play.
In this case, it appears Player 2, in an effort to speed up play, short-cutted the word "call" and went straight into the showdown. Showing your hand in response to a shove (an all-in raise) is definitely considered a call by poker pros.
When there are only two players left, player 2 showing his hand hurts him and no one else. Thus you can just ask him to make an official move (i.e. actually call), and then proceed with the game. This would work even if the previous bid wasn't All In - player 1 could continue playing with full knowledge of player 2's hand, and player 2 has only himself to blame.
If there are more than two players left, however, showing your hand is unacceptable because it tells the remaining players things about each others' hands (i.e. which cards the others are not holding).