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 consecutive all-ins.
Win a hand with a Straight Flush.
Knock out Max after he's bought in with his special item.
Win a pot with two or more opponents when you are all in.
Knock out Tycho after he's bought in with his special item.
Win a game on hard.
Win a hand when you have three of a kind comprised of three kings (of any suit).
Knock out Strong Bad after he's bought in with his special item.
Knock out The Heavy after he's bought in with his special item.
Win three straight pots.
Win a hand with Four of a Kind.
Win a showdown where you and the opponent have same hand (pair or better) and you have a better kicker.
Win a hand with a Full House.
Check a pat hand.
Win 12 or more hands.
Win a full game.
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.
Win a hand with a Flush.