Worst I've seen was in a STT at UB. Thankfully I had folded so wasn't directly involved in the hand. (Sorry for mentioning an online event in the Home forum.)

blinds are 100/200
MP has 800 chips left and limps in with A[img]/images/graemlins/diamond.gif[/img] 2[img]/images/graemlins/diamond.gif[/img]

BB has 4000 chips with J[img]/images/graemlins/heart.gif[/img] 6[img]/images/graemlins/diamond.gif[/img]

Flop: 3[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/diamond.gif[/img]
MP has a straight flush and goes all in.
BB calls.

Turn: 7[img]/images/graemlins/diamond.gif[/img]
BB makes his higher straight flush.

River: irrelevant

That's the worst I've seen. Busted aces, trips, and full-houses and even quads can't be as agonizing as that.