The Worse Band(s) You've Ever Seen in a Live Environment

Simon - Monster Magnet opening for maiden in Chicago was at the Aragon (Not an arena).
This was supporting Ed Hunter, so before Brave New World was even recorded.
So many long time fans had no clue he was even back.

I saw this pairing at the Rave/Eagles Ballroom in Milwaukee...
Coincidentally my worst concert experience ever, even worse than being puked on @ UFO/Saxon at the Amphitheater.... It was SO damned hot in that place, and as you might expect, it was PACKED......
 
Monster Magnet can apparently suck live. Two friends of mine, both huge MM fans, drove down here from Tennessee to see them, all happy about it.....and then they left the show, almost in tears, about halfway through MM's set because they were dreadfully loose and painful to watch.

As for Star People.....well, the "Star Girl" was kinda cute. :) (Still one of the oddest opening bands I've ever seen on a rock bill. They were better-received when they opened for Ozric Tentacles on tour and were cool to hang out with backstage, too.)

MM was SOOOOOO bad....me not liking them, plus the OFMF (opening for Maiden factor), plus the heat, probably didn't do much for me overall. I never liked them at all, and this further cemented my opinion.

LOL @ Star Girl......yeah, that was just WAYYYYY to weird, even for a dude who likes and appreciates "weird" music....
 
Slayer at Ozzfest 2004. No tone, it sounded like they were just pounding on shit and the mix was horrible, like there were mattresses on top of the speakers. muddy and just awful sounding.

They were following Dimmu who played circles around EVERYONE that day.
 
Blind Guardians first US appearance. They were all zombies on crack or something.

I saw their first tour when it played Detroit and I don't know if they were nervous or what, but it looked like they didn't even know what to do (especially Hansi). The reason I chalk it up to nervousness or uncertainty is because they've been much livelier in the tours since then.

I've also seen that with other bands, including Necrophagist. Muhammed looked like he was reluctant to even talk between songs on Carving North America's Epitaph in '06. When he did talk, he mumbled and basically did not seem very confident. But I've heard that he's pretty active and energetic on stage since then.
 
I haven't read all 9 pages of this thread so I don't know if they have been mentioned or not, but the worst band I saw live (and they sucked major ass all 3-4 times I saw them) was Ratt. We walked out on them after a few songs the last time because we really only went to see the opening band, Kix.
 
Anthrax

Opening for Judas Priest. It was so loud in the hall that you couldn't make out anything. Even with earplugs, and being off to the side, I thought Commotio cordis was a distinct possibility. On top of this, sitting around some real douchebag fans made the whole event suck. Luckily JP came out with a lower/better mix, and were the usual awesome; so the whole evening didn't completely suck.
 
Dokken...not the band, but the man. Saw them last year open for Scorpions. I loved Dokken back in the day, but based on what I saw/heard Don needed to hang it up decades ago.
 
Anthrax

Opening for Judas Priest. It was so loud in the hall that you couldn't make out anything. Even with earplugs, and being off to the side, I thought Commotio cordis was a distinct possibility. On top of this, sitting around some real douchebag fans made the whole event suck. Luckily JP came out with a lower/better mix, and were the usual awesome; so the whole evening didn't completely suck.

When I saw Anthrax (opening for Dio in 2005) they killed. That was a great night of live metal.