My worst recent pug experience was in one of the troll heroics. The tank and I knew what we were doing but we got stuck with three dps from the same guild that had to be some of the worst players I've ever seen.
None of them knew any of the fights and pulled between 5-13k on boss fights. They didn't get do a single interupt or let a single cc run its course. We patiently explained each fight to these three dps and they didn't say much until we got to zanzil. The tank went down almost three minutes into the fight for some reason or another and they hadn't even gotten the large berserker add down yet. At this point the tank lost patience and asked why it took so damn long to kill an add. They immediately started spamming insults in caps about how the wipe was either the tanks fault or my own. My favorite was that it was our fault the fight took so long. Apparently when they normally run that instance the fight only takes about two minutes, and our tanking/healing stretched it out. The worst part was that through all their previous runs through the instance they hadn't learned how to execute a single fight properly.
As a tank I've had random dps start marking targets without saying anything and complaining about what a terrible tank I'd been. Someone else actually initiated a votekick on him before I could type in a reason.
---------- Post added 2011-07-18 at 08:43 PM ----------
Reading some more of these reminded me of another one. I had a pally tank with two guildies in the stonecore that couldn't figure out how to avoid groundslam. Turns out he didn't know when it was about to cast because he didn't have cast bars enabled. The run started with a skilled healer getting kicked from the group for calling out the dps for not doing their job on the first boss, so even after the two bad dps quit we couldn't initiate another kick.
Our fourth healer quit because the tank had less than 100k hp. Turns out he didn't realize all his gear was red. He refused to drop group, so when one of the dps left we convinced him to reque as dps. He checked the dps box but didn't uncheck the tank box, so we didn't get a new tank. When another healer left he qued as dps and didn't understand why we couldn't que as a group with four dps. I think we went through six or seven healers and I don't know how many dps during this run.
Over the course of the instance the tank had been mocking someone for pulling 6k dps. This was a time when people weren't geared, so 6k wasn't good but it wasn't too terrible. When we finally got a new tank and the old one went dps he wound up doing less than the person he was complaining about. We didn't let him forget about it.
He finally wound up lagging out right before the final boss and it let us initiate a votekick. I normally don't take pleasure in kicking someone, but this guy deserved it more than anyone else I've ever met.