They might know how to play their class. They might know the fights. They might not stand in fires. But they can't play the social half: they don't interact well with others. They are as incapable of being useful raid members as any noob; not because they fail at the raid, but because they fail at the social actions necessary to get into the raid, whether that means getting into a PUG or a guild.
Maybe they're selfish assholes. The guy who ninjas stuff from HToC-5 to vendor it. The trade chat flame-war-starter. They just don't care about other people. The solution is obvious: shoot them. Okay fine, maybe there aren't enough bullets. Or, that would be a horrible thing to do, pick one.
In actuality these people may not be universally horrible. Instead they may suffer from distorted perspective. They see everyone as a noob who deserves nothing. They think a joke was an insult. This is actually a growing view on the cause of bullying: bullies interpret nonthreatening gestures as threatening and react according to their misinterpretation. What's to be done with this? Talk things over with them, ask why they did what they did and politely point out the flaws in their reasoning and perceptions.
Or ignore them and flame them in trade chat so people know to avoid them. This is probably much easier.
Other people might be bad communicators. They are the anti-Reagan: can't communicate, but might have something worth saying, if only you could get through their online speech disorder. There's a place to start: don't flame them for bad grammar or spelling, but instead attempt to convey to them that poor writing in a text-based environment has the same effect as a speech disorder: it makes them hard to understand. Encourage them to slow down and enunciate, spelling out words and using punctuation when it will reduce ambiguity.
Some are such bad communicators that they might as well speak another language. They are the ones who don't type or talk ever. Or they are so delayed that they might as well say nothing.
Then there's the worst of all worlds combined: the guy who accidentally pulls adds during a boss, wipes the group, then goes afk and is unresponsive while everyone runs back. He doesn't respond to party chat about what happened to him. Instead it is only when you're all back and he's demanding a res that the situation becomes clear: he needed to go smoke a bowl. I don't mind the drug use. I might not even mind him going away to smoke and asking for a res. Maybe a little bit. What really bothers me is the non-communication. Disappearing, going silent, and then acting as if he did nothing wrong.
This is the final type of social noob: the person who is utterly incapable of understanding that his actions negatively affect others or of accepting any responsibility for problems. These are the people who I kick from the group at the drop of a hat. They are the people who refuse to run back from wipes, the people who justify ninjas with "it's just heroic", the people who show no consideration for others beyond taking the time to argue about how they have done absolutely nothing wrong.
WoW is more than just a game, it's also a social world. We interact with others. To get far we must interact with others. Those who can play but not communicate will not get as far as they could. Can we save the social noobs from themselves?