I consider myself relatively slow to anger and tend to not bother too much with the less pleasant kinds of gamers I deal with both online and offline. However, there are gamers that do annoy me to no end. Lots of them, I'm going go through an overview of the types I can recall off the top of my head:
I hate "HARDCORE" gamers, well elitists in general. Whether they're console fanboys, PC "Master Race", or HARDCORE, I hate them. Why? Because it is fine to have a preference of games you like, whether its a type of genre, platform, or difficulty, but it becomes just maddening to see someone complain about games that are *GASP* made to appeal to another person other than the preferences they have!! "OH MY GOSH! THIS IS HERESY!!" Hey platform fanboys, not everyone owns every platform to play games on (PS3/360/PC, I don't care that much) and playing on something that you don't doesn't make a person "inferior" in intelligence or taste. It just makes you come off as an elitist prick.
Hardcore gamers are THE WORST in this category, screaming bloody murder at the thought of games being made for people who aren't that passionate/experienced/knowledgeable about gaming. This generation revolutionized demographics that way, making games that people, like say, my aunt, my teacher, or other people who haven't touched a game, or that many at all in their life and were initially intimidated by complex user interfaces (Read: controllers appear to have too many buttons for their tastes) or very steep learning curves. What these people tell me, is that these people don't deserve to enjoy our hobby and have fun at all because they're not "REAL" gamers with the same preferences and passion for us. And that companies who make games for them, like PopCap, Nintendo, or Natsume, should go die because they're "ruining" the game industry by expanding the market. . Seriously, I hate these people more than I do the platform fanboys. They can go to hell.
I know someone on this thread linked TVTropes, but I can't think of a better term for these people, the "Stop-Having-Fun-Guys". Whether it's a fighting game, FPS, or MOBA game, competitive games tend to have intense, complex meta-games with tons of different strategies and techniques for success. But then there's this asshole. Regardless of his actual skill at the game, you're going to dislike him for the arrogant mentality the he (or sometimes she, but its not common) carries. He's a poor sport, constantly insults his teammates, and is constantly criticizing his teammates or sometimes opponents for not using the "right (as far as his head is concerned" strategy/character/item build/whatever to win. As far as I know, and due to the nature of the genre, these guys are even worse and FAR more common in MOBA games like League of Legends. They often kill morale and structure in a team because instead of fixing/adapting on the fly when things go wrong, they won't stop bitching and arguing at their teammates instead of, oh I don't know, actually help them?
"Gurl Gamerz" as we call them are obnoxious, but they seem more like an obnoxious stereotype if anything because I've never seen a girl who fits that category (i.e. advertises her gender like its a status symbol and screams misogyny at guys who don't give her the attention she wants). In fact, the female gamers that I do know not only DO NOT act like that, but actively hate girls who do do that.
"12-14 year old racist/homophobic children with microphones". This stereotype, I don't get. Why? I don't seem them too often. When I do, I either mute them, or come up with a witty retort, since, they're children with the vocab of dirty-mouthed 3-year old parrots, knowing little of the words they're saying to people, and they have the life experiences of well... children. It's easy for me to make fun of them to deal with them when they do come up... and it is not often.
On the OTHER HAND, I more often than not (LoL, WoW, Xbox Live, PSN, wherever), deal with 20 to even 30 somethings who behave in the same manner. In fact, foul-mouthed, bigoted man-children are far far more common and far worse to deal with, but also more pitiable, but still... I can deal with a little delinquent preteen, but a 20 something who acts like that, spouting racist remarks, the tired "your mom" remarks, and generally acting like homophobic pricks will always be more obnoxious by virtue of being older, presumably knowing better, but not.
I hate "nostalgics" who believe everything was better in their "hey-day" when they haven't actually gone back to pick apart everything from that era and only have their rose-tinted nostalgia lens to look through. Pokemon fandom suffers enormously from these kinds of people (although its been getter better nowadays). Let's see... nearly all of these people had played Pokemon at some point of their lives, the first two generations, and loved them, but then dropped out of the franchise when the third generation hit and the Pokemania fad had died down and the anime (which was watched by many) had begun to be seen as stale. Now these people come back, see changes (including new mons), hate the changes because its not "exactly" the same as they remembered it, and often throw the "out of ideas" phrase without actually proving why. If they actually looked into the newer games, and compared with the older ones, they'd find that: 1. These new Pokemon, Gym Leaders, mechanics, moves are not only here to stay, but some of them are welcome changes and additions to the franchise that keep it fresh while still feeling familiar and 2. The old games haven't aged that well, AT ALL. The Game Balance in the original Red/Blue is crap (Psychic type ftw), there are numerous glitches existing in the games, mechanics that we don't miss in the newer ones (Does anyone like HMs?, or mind one use TMs?), and crappy Pokemon that have existed since the beginning (Heh, did you actually use Farfetched at all? Did you want to use him back then?).
Yeah, you can't argue with these people, since they're too damn stubborn to take the damn nostalgia goggles off and see if their nostalgic treasures truly stood the test of time.
One thing many of the worse kinds of gamers have in common is the inflated sense of self entitlement they all have. The "It's all about me and what I want" mentality leads to the platform fanboyism and "Hardcore" gaming mentality that leads them all to think that "game developers should make the games that I want and nothing else. Anything that isn't that is just a bad game".
Yeah. I hate these people, but its a shame that a lot of sites and publications cater to these kind of people *COUGH* Game Informer *COUGH*.