SD: Kryxix, Executor Tarvold, Grand Proctor Beryllia, General Kaal
DoS: Hakkar, Manastorms, Xy'exa, Mueh'zala
SoA: Kin-Tara, Ventunax, Oryphrion, Devos
PF: Globgrog, Dr. Ickus, Domina Venomblade, Margrave Stradama
HoA: Halkias, Echelon, Ajeez, Lord Chamberlain
NW: Blightbone, Amarth, Stitchflesh, Nalthor
ToP: Affront of Challengers, Gorechop (meat hooks), Xav (arena), Kul'tharok (Lich after portals), Mordretha (naga)
Mists: Ingra Maloch, Mistcaller, Tred'ova
Streets: Zo'phex (rotating body), Grand Menagerie (blue balls and spinny whirlwind), Mailroom (briefcases), Myza's Oasis / Zo'phron (instruments), So'azmi (shape teleporters)
Gambit: Hylbrande (titan), Timecap'n Hooktail (Our cap'n is a dragon!!!), So'Leah (explodey orbs, collapsing star)
I had to do my best to guess what people would vote for, max 20 entries.
I'm guessing not a lot of Halls of Atonement, Spires of Ascension, or Mists of Tirna Scithe bosses get picked although I bet there's a few that despise Mistcaller (she's a pain on explosive). Maybe Ingra at high key levels, I dunno.
And Devos' spear that can bug some times will get at least a few votes.
I felt a need to list most De Other Side and Necrotic Wake bosses, I really think NW in particular has four bosses that all are quite punishing of one mistake.
Taza'vesh also has some fairly nasty ones, Menagarie, Mailroom, Timecap'n, and So'leah I've all personally had some fail groups on.
My pick for #1 most hated by others is Timecap'n Hooktail. The tail swipe is enormous, the breath is super touchy for the tank (she moves differently than most mobs I swear), the fires are everywhere, it's just a mess.
I personally wrote this post because I can't stand Gorechop, although after a year it's not quite as bad as it was. The collision detection is still occasionally BS though!