Your Enemy's "Psychic", Plus He's My Greatest Work So You're Not Allowed to Kill Him
This DM has a favourite NPC, sometimes a villain that you want to kill, but you just can't hit him no matter what. The DM's not even rolling for Reflex or Will saves.
PC1: I cast Fireball.
DM(without even rolling): He leaps out of the way and out of range of your spell.
PC2: While he's dealing with the wizard, I send a couple of arrows his way!
DM: It won't do you any good. He'd already cast Protection From Normal Missiles.
PC2: When?!?
DM: Right before you guys entered.
PC3: We snuck in AND won the initiative!
DM: So? The guy's paranoid. What can I say?
PC4: I know what I can say. 'I quit.'
DM: You're just mad 'cause your losing.
Sure you can do that
Has no cohesive setting, or it changes from week to week. Anything some players say is obviously in the setting, or it would be really cool if added so crappy homebrew rules are created on the spot to include it-7 sessions in- (guns, air ships, new races, ect) but when other players attempt to make basic assumptions that were never specified to be different (Ill just be some sort of wood elven archer) it is treated as though this was an obviously stupid question and ridicule starts. (I was one of the favored players, but it still bugged me, although mostly because it would be because crappy homebrew rules would be created and then id be obliged to use them)
Flavor=mechanics
"Sorry, no arcane magic in this game you can't be an eladrin." I can't see how you could justify fey step as a not arcane thing. "What if it were he is really acrobatic and he leaps/hops/tumbles over to where he would normally teleport". Also call it a high elf, or heck I can even use the fluff of normal elves. No dice, well what if you houserule that eladrin soldier is open to non-eladrin because I mostly just want to play a spear user honestly. No? Thats not even remotly arcane.
Skills dont matter
Discourages the use of skill checks, especially social ones. Would prefer you "roleplay it out", and then arbitrarily decides if you succeed or not based on a whim.
4E is basically the same as 3.5, I won't bother reading the changes
Claims to read the new book, and love the new system so much more, while in reality DMs using the old systems rules. IE feats are assumed to do what they used to, monster special abilities, racial powers, classes (I assumed clerics get plate), magic items (+3 flaming frost longsword that adds d6 of each type on each hit anyone?) Will occasionally reference the BAB (or equivilent) of the players, who often times have never played anything but 4e, and is confused when no one knows.
One big monster
All you ever fight is one big monster, so every fight is either cake walk, or a TPK. Results in DM escalation of monster levels, skewing it closer to TPK every fight. Rarely more than one foe.
All NPCs are better than you
All the NPCs are better than you. Not only do you get the impression, but you are told. In character. "Greetings, I am ___ the fighter. I will train you. Go see ___, my level 23 apprentace fighter."
The Frankenstein
Combining disparate elements and themes into a coherent story can be done well, or it can be done in the Frankensteinian way, where a DM will take various settings, books or genres kill them, rip them apart and then stitch them back together into an unholy amalgam of a campaign setting. "They called me mad...they said one couldn't combine World of Warcraft's setting, Rainbow Brite's characters, Warhammer 40k's storyline, the themes of Adam West's Batman into a working setting. But I showed them! MUWHAHAHAHAHAHA!"
You'll Have To Improvise
This one isn't so bad so much as it takes getting used to. He won't tell you the rules, and refuses to let anyone look at the combat rules in the PHB. If you ask him if it's possible to do something under the rules, or if he has any house rules about it, he responds with "Why don't you try it, and see?"
This DM either doesn't like the existing rules, or hasn't read them, and doesn't like the players being aware if it's even mechanically possible.
The DM that does't want to be there
Does everything in his power to make the game end as fast as possible. Including allowing you to bypass the puzzle to open the secret door and head down the stairs, only to have you ambushed by 3 goblins who automatically roll crits in the surprise round. Then when you try to jump over whatever they're hiding behind, it bursts into flames and kills you without allowing you a save.
Hey, let's give this a try!"
No campaign lasts more than 2 or 3 sessions under his rule. Every third week, he thinks up something else for the players to try, using new characters in a new setting. Often gets bored quickly, or has too many ideas floating around to form a coherent, lengthy storyline.
Mr. Improv
Rarely has anything planned. Most encounters are decided on by him pulling out a Monster Manual and flicking straight to the back of the book, where the creatures are listed by level. Usually starts a new campaign by rolling a d10 and saying, "Start at this level" (The d10 roll).
"4th Edition? Pfeh! I can't make Homebrew, so we'll play 3.5."
DM flat-out refuses to play 4th Edition. Why? Because he's got too much homebrew created for 3.5. Rather than take the time to learn how to balance out homebrew things in 4e, he declares that the group will continue playing 3.5 indefinitely. He promises to learn how to homebrew 4e stuff, but it won't happen.
4E Fanboy
This DM thinks 4E is the messiah of D&D and will purposely destroy his 3E campaign world in some apocalyptic cataclysm. He will only run 4E forever more, refusing to play 3E despite his players prefering 3E.
The Purveyor of Inconsistant Reality
This DM doesn't make any effort for his encounters, or even worlds, to make any sense whatsoever. Attempts to make logical conclusions based on what he throws at you always fail, because there is never any thought behind it. You encounter Hydras in rooms that do not have exits big enough for them to leave and no sources of food, prides of lions on pyramids in barren deserts, polar bears in the swamps, Human bandits who liv in pitch dark caves without any lights, etc. Most often this is done when a DM just wants to use specific monsters against the PCs, which can lead to ridiculous combinations of forces for you to battle (like, oh, Drow and Pixies) simply because the DM thinks it's cool. This can get even worse if it extends to the DM's wold itself, which generally results in any conclusions players make based on the descriptions the DM gives to be about as accurate as it would have been to make a random guess. Traps work because the rules say they do rather than because of any actual mechanism, all of the habits of that evil cult you're hunting as told to you by the DM are just fluff and any attempt to act on that knowledge results in failure, and gods help you if you try to follow the world's political system...
The Dragon-Slayer Campaign DM
Ever fight a dragon every session? Either the DM really likes dragons or he just cannot handle creatures that aren't solos. Either way, the entire campaign is based on slaying a different named dragon every session.
All characters have in-depth backstories involving their dreams, aspirations, vocations, etc. but once you enter his world, you're murdering dragons.
Too late, you should have known what i meant
The DM who fails to give an adequete description of the place/situation you are in, and then punishes you for taking actions based on what he said rather than what he meant to say.
example: You come across a room in which you believed the floor was trapped, there were lit braziers on the othe side of the room. You threw my grappling hook over to one of the braziers, but apparently these braziers were 10 feet across with a fire burning hot enough that it burned through rope before your DEX 20 halfling could react. So you lose the grappling hook because you thought you were throwing it into a regular sized item rather than a massively oversized one. Then there are situations were a 10 foot deep inescapable ditch turns into a waist high one instead during the middle of combat, and you are not allowed to take your action back of course.
End of the World Man (aka: 'Screw it, I can't take it anymore')
Has no ability to adapt to players. It's his way or the highway, and if the player goes off and deviates from the DM's path, he detonates the world and ends the campaign right there. If the party is too strong to get through his encounters, he declares that someone (Or everyone) is playing a broken character build, and ends the world to make you cut it out.
Hurry up and kill the monsters!
At the start of each encounter, tells you how many hit points each monster has, what it's weaknesses are and what your battle strategy should be with very little role playing because the session has to have 4 encounters by 9 pm. "What do you mean, you want to talk to the dragon??"
Setting Fanboy
Has every book, read every novel cover to cover. Believes every other setting is bad. Tries to make players into stereotypes of the setting. See also "Dritzz clone". Believes that everything non-preferred-setting, non-core book is tainted in some way. "Does not exist in X setting", "They are all power-gaming", and such.
Much of this does not apply do Eberron fanboys.
You're perrty
The DM that has a crush on one player in the group and obviously favors her over the rest of the players.
"You find a +5 intelligent dragonslaying katana made of pure gold."
<yawns> "Ok, I'll hang it on the wall of the castle with all my other ones"
"Um...so I'm 11th level now and I still havent found any magic items."
"Oh...you...yeah...um...you find a +2 short sword."
"Are you ****ing kidding me?"
"Ok ok, you find two +2 short swords."
The um... wait...umm.... sorry...just a second...
Runs a pre-published adventure and hasn't properly prepared. Doesn't really know what the players are supposed to be doing in said adventure, and so neither do the players. Constantly stalls the action to refer to notes about the adventure. Fails to give vital clues to the adventurers as to the objective, scene, motivations, etc. Read's the read-aloud text, and then is done.
Players eventually give up and just kill whatever happens to come along.
This guy and that one...
"You walk into the hallway and you see this guy..." - puts miniature on table
"The room is full of a bunch of these..." - puts miniature on table
"This guy attacks you..." - points vaguely at the miniature somewhere on the table.
Especially bad when combined with "The um... wait...umm.... sorry...just a second..." DM because not only do the players not know what they're doing, or why they're fighting, they don't even know WHO they're fighting.