What's been your biggest loss in poker so far? How did you play the hand, what were your thoughts behind it, what would you do differently if you could play it out again?
Post it here and see what others have to say.
I'll go first -
Checking PokerTracker, my biggest loss was $52 in a .25/.50 NL game. (ouch....)
I was on the button and found

. One player calls the BB, another raises to $2.25. I call along with the intial caller.
Flop comes
It's checked to the raiser who bets $15. I raise to $30. The checker calls, going all-in. The raiser re-raises all in for nearly $50, and I call, putting me all-in.
Turn is

and River is
Showdown? The pre-flop raiser had

, and the EP checker had

.
My mistake? I should have put the raiser on an over pair, given his pre-flop raise and the strength he showed on the flop. I believe my thinking that was that as far as the flop texture was concerned, my 9s weren't such a dog, and that I needed to bet out any drawers. Of course I didn't think about the fact that a lot of hands beat my 9s, and since it had been raised pre-flop...I should have figured that one of them was out there.
My biggest weakness has always been stubborness and not giving my opponents credit for a real hand.