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 a Straight Flush.
Win a hand with Four of a Kind.
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 game on hard.
Win 12 or more hands.
Win a hand with a 6 card and a 9 card of any suit.
Knock out Strong Bad after he's bought in with his special item.
Win a pot with two or more opponents when you are all in.
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.
Win a hand with a Straight.
Knock out Max after he's bought in with his special item.
Win a hand with a Full House.
Win consecutive all-ins.
Win a full game.
Win a hand with a Flush.
Check a pat hand.
Win three straight pots.
Win a showdown where you and the opponent have same hand (pair or better) and you have a better kicker.