Many years ago I joined a game that was run out of a game store. The GM was a long time friend of the owner and while the game rooms had to be booked he pretty much had the largest room booked to run a differant game everyday. Miniture battles, card games, ect. Friday night was RPG night and he was running D&D. And this led to problem one. He was running forgotten realms in 3.0, dropped the core book and players guide on the table and we could build anything as long as it was book legal to just these two books. This was a problem at first because he had sucked in 11 people to play and we only had 4 copies of the faerun books between us. So 3 hours later we all have characters, he looks them over and tells everyone who has an alternative race or class from the Player's guide we weren't allowed to use them. While irritating, it was still just annoying not terrible, but did seem a beginner mistake from someone who said he had been GMing for years. So new characters in hand, a short backstory outline, that he insisted we write out for him right there. The characters were to start at 3rd level, which was fine with me, and he 'randomly rolled' a single magic item for each of us. Also fine, even if most of us got items that weren't terribly useful for our characters, he also forbade us trading our starting items.
This irritated us as example my character was a sorcerer and my item was a cleric scroll, I literally had no use for. Then characters were introduced and one of the players, who was the GM's roomate, has a fighter wearing Demon Armor. Which he proclaims loudly. We don't think much about it at the time, thinking its just favoritism on the magic item. Then the 'adventure' starts, which pretty much is a fetch quest so we can hit a dozen random encounters. Every attempt to roleplay with NPCs turned into him telling us the outcomes of talks but never having them. His 'adventure' turned out to be a plot from a novel he cribbed, which while not that bad on its own he kept changing details on us. Every game there was no scripted combat, he just used a random encounter generator on his laptop for it. So a railroad plot, that kept changing track, withstops for randomly generated combat. And randomly generated Monty Haul worthy loot.
Thing is even for our large party the encounters seem over-powered, lots of damage reduction we can't overcome, ridiculous AC we basically have to crit to hit. Except for his roomate and two other players who were already his friends, they just breeze through the encounters that are slaughtering the rest of us. Someone finally asks and finds out the three of them have 8th level characters and scads of magic items. With the generator he was using that made our party level 8.5, if we were all the same leve 11 level 3s would have been 5.6.
The DM starts the next session telling four of us not to comeback to his games for being angry about this. A fifth player left a session later after realizing the only reason he wasn't asked to leave was his character had the artifact the entire campaign was based around. And the Dm didn't think of just giving it to a differant character.
We soon started our own game, and the players from his game stopped by cause we were in differant room and discovered we were having fun without bowing to him. He tried to get the game store to ban us, but we did nothing wrong so the owners told him to mind his own game don't worry about ours.