The worst-played hand in Texas holdem is 3,2 suited.  People lose more on average with it than any other.  It is not the worst hand, but it is the worst played hand.  Why is it so bad?  The potential to make a straight or flush dazzles people into playing it too often for too many bets.  The danger is you may actually complete your draw and bet big -- 3,2s can only make the lowest straight or flush. Opponents willing to call multiple bets will have a flush or straight just like you -- but higher.  So the hand usually loses just when there is a lot at stake.  3,2s is the sort of hand that wins tiny pots but loses big ones.  Further, if you make three-of-a-kind, it is the lowest possible.  Even if you start out ahead by flopping the only pair, virtually all subsequent cards are threatening.

This is a chart of how well people played their two-card Texas holdem hands.  It shows how much was won or lost in 16.6 million actual hands of limit holdem played at the PokerRoom.com.  All 169 hands are arranged by type, along with their rank and how many bets they won on average (the EV, or expected value).

EV is "expected value" in big bets.  So the average win with a pair of aces (A,A) was 2.44 big bets.  A,A ranks number one as the most valuable hand to hold.  Looking at the bottom of the pairs column, you can see that 2,2 lost money on average, and was the 67th worst hand.

Since this is real, not theoretical data, there are plenty of surprises.  For example, everyone knows that 7,2o (seven, two offsuit) is the worst of the 169 holdem hands, but it is only 128th in actual loses.  A,2o is seemingly better, but at 162, it actually loses more.  This is because people rarely play 7,2o, so they lose little.  But they play A,2o enough to make it one of the most expensively misplayed hands in holdem.   It makes the smallest possible straight, and if you have the misfortune of pairing the ace and betting it, then all other ace pairs have you out kicked (unless there's another sucker playing A,2o, in which case you still don't win anything, just break even).

Just because a hand has negative expectation on this chart does not mean it must never be played.  Most people do lose money with the pair 4,4, but experience shows it has positive expectation when played in late position in an unraised pot with several previous callers.  It will also do well against a single opponent whose high cards have not paired.

Identifying the worst hands.  Combing through this data, we can spot which hands people are losing the most money with.  (This is easier to see in the other version of the chart down below, where hands are arranged by value, not type.)  Note that the seven most expensive hands (163 through 169) are all suited.  Clearly, people have trouble throwing away suited crap.  People are also mislead by the potential of small, unsuited ace connectors.  The hands A,4o, A,3o and A,2o are major losers.