Our top vote would have to go to Fame - poor performance, nutty dispositions, and females that didn't milk well. We also did not get along well with Roth's Millcreek Unique or 8180. Unique didn't have the growth and 8180's didn't milk like we thought they should either (but they looked good and had good REAs).
I know I'll get a lot of disagreement on this one, but 878 did not do well for us either - above average carcass (good REA, but higher fat) and all but one calf (who we made a steer because he lacked performance) had temperament problems. Have one 878 female left only because she continues to at least raise (below average, but alive) calf (and doesn't try and kill you when you work it at birth - because she runs away) - has such a flighty disposition we have nicknamed her "Tennessee" (as soon as she sees you, she'll raise her head and trot off like a TN walker horse) or Rocket - She is also a head gate jumper and extremly nervous in the chute. As soon as she's open, she'll be gone. I know he must have worked well for someone, due to the high volume, but he did not work in our herd...
I'm surprised no one has mentioned Sleep Easy...another quite popular bull that lacked in some areas.