As for RPG nerve noodles, I have had the honor of playing with quite a few of them. However, one has to distinguish between online and pen&paper RPG, because quite a few problems are specific.
The folks that have omnipotent indestructible characters and just MUST win every fight. Powergamers.
People who have no sense for spelling, grammar or punctuation. A minor case of this is people who know no formatting. Often they write well but their format is horrible.
The know-it-alls. So, I want my Klingon to sing the McDonald's jingle in a pink tutu with a pet shark on the arm on top of Mount Seleya right next to Elton John? And I post it to make someone laugh? Oh boy, am I in for a lecture about Klingon culture! And what the hell do I think to have a female Klingon with status? Shame on me!
People who start a game and then leave.
People who want to steer the game all by themselves and complain when my characters have their own mind.
Guys who want to cyber all the time. Girls are just as bad but not as plentiful.
The worst: Empty posters. So, you see they post a decent amount, have decent spelling, gammar and such, have interesting characters but as soon as you start playing something meaningful, you realize, their posts are void of any sort of meaning. This is especially frustrating because you thought you could actually accomplish something with these people.
The elitists. They think they're better than most players. I know I sometimes fall into that category. But I never look down on anyone.
Pen & Paper twerps
The worst horror of pen&paper games is to find a GM that is good. So here's a list of GM troubles.
Those who have favorites among players.
Those who are unprepared and cannot wing an adventure (I have been known to have that flaw at times).
Those who must "win" at all times.
Those who stick to their stories too tightly to see the adventureres aka players take a different route.
Those who don't understand the system they are playing and keep reading the rules at every roll.
Those whose adventures are little more than just combat, or the other extreme, nothing but boring politics.
Those who insist on every rule even if it is silly.
Those who just love to kill PCs.
Those who use their position to introduce their own PCs, which are hopelessly overpowered, before a guest GM takes over.
Also, there are a lot of players who can make our lives miserable.
Those who want extras all the time.
Those whose brave heroic knight is a chicken. What I mean is fear of taking damage.
Those without a sense of character. Said knight-chicken allusion for instance. They just don't get that a knight should be brave.
As previously stated, folks who always play the same person or, worse, themselves.
The ones who assume command and want to run the game and you get no say whatsoever in what the party does. Usually, I and one or two other players then go rogue
The ones who spend the game in slumber until they are told to do something.
People who are absent all too often.
Okay this was a short brainstorm
You don't ever get a perfect group and GM. You will always have all these problems in your group. But the basic thing is the balance. Not every player is an RPG genius and socially adept. In fact, I still have to meet one.
As for my personal pen&paper position, I think I am a decent GM. My stories are skeletons of NPCs who have their own agenda and places where to find them (or not). My adventures move around the player's actions. So they are looking for a murderer? Heck that murderer has found out! Now he works against them! Shucks, they go into the barn where he killed the maiden. Hmm... so he follows them and sets it on fire MUAHAHA! Get out of this one, fools! Of course the players then realize the murderer followed them and ooops, he lost ground rather than winning some. Curses and other honorifics.
As a player, I try very much to stay in character. I like the challenge of playing someone I'm not and someone who's different. I usually play women but have been known to play a few nice guys as well. My online characters usually have more flaws than edges, one even is a collection of flaws with just one minor edge. My starship captain has lost a leg and has been wearing a flawed prosthetic for over a year of real time now because he hasn't had a chance to get to starbase to get it fixed. My most charming male character is homeless. My powerful warrior is haunted by the ghosts of the past and my huge ogre is so dump he thinks he has a pet cow with changing color because he doesn't get that the things keep running away and he finds new ones. The last WoD game I was in I knew from the start we were dealing with Vampires but my C didn't. I acted accordingly to my C's thoughts. That was SO much fun
Life is very similar to boxing. Defeat is not declared when you fall down. It's declared when you can no longer get up.
Some people just want to watch the world burn... not because of the pretty colors but because after the fire, there comes rejuvination.