Here is the full list of all 20 Poker Night at the Inventory achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Win a hand with Four of a Kind.
Win consecutive all-ins.
Win a hand with a Straight Flush.
Knock out The Heavy after he's bought in with his special item.
Knock out Tycho after he's bought in with his special item.
Knock out Strong Bad after he's bought in with his special item.
Check a pat hand.
Win a game on hard.
Win a hand when you have three of a kind comprised of three kings (of any suit).
Win a showdown with just a high card.
Win a hand with a Straight.
Win a hand with a 6 card and a 9 card of any suit.
Knock out Max after he's bought in with his special item.
Win 12 or more hands.
Win a hand with a Flush.
Win three straight pots.
Win a full game.
Win a showdown where you and the opponent have same hand (pair or better) and you have a better kicker.
Win a pot with two or more opponents when you are all in.
Win a hand with a Full House.