With one, only one exception, every single moonkin I meet in game is either bad at his class, rude, or both. I do not know what causes this. It's not a pre-existing anti-moonkin bias which causes me to negatively interpret neutral phrases. No, that is (actually by now, was) reserved for arms warriors and all classes of hunters. That list has since changed, with no hatred for arms, less dislike of hunters, and the addition of rogues. My point is that moonkin are jerks and/or noobs.
The first one I met was a jerk. But, I decided to go against my instinct and not make a fuss about him. He rode the epic train in my guild until we got to the slightest challenge, then ran. In retrospect I should have recommended that he be gkicked and blacklisted months back.
Then there was a general assortment of jerks in PUGs. There weren't a ton, since fortunately moonkin weren't and still aren't very common. Still, even with a small sample of only a dozen or so, a 100% occurrence of jerks seems to indicate something.
The exception continues to confuse me. He's a moonkin, but he's neither a jerk nor a noob. Fascinating. He's in my guild, but as the first example shows, that's not always a guarantee of positive ratings.
Most recently is was the jerk in a PUG with my priest. The situation was a bad tank who didn't talk much, which put him squarly in the middle of the group. The other people were a mage that didn't talk much, but could reliably sheep and eventually found her iceblock key, a shaman that started off the run by whining about a harmless fear (which saved the mage), and a moonkin that had no concept of aggro, off-healing, off-tanking, or shutting up.
So the tank pulls a bunch of mobs, or a pack and a pat, either way, there were too many mobs for him and I ended up with one on me due to aggro*. Seeing as no one except me was dying especially fast, I MCed one and set it on the other. Not a normal technique, but all the mobs died and all of us lived. As any good player knows, there are only two types of healing: enough and not enough. Seeing as I did the first, clearly I'd done my job. But no, the moonkin and shaman still didn't understand the concept of shutting up.
So, I suppose that's that. In my entire experience (that I remember, so I suppose that narrows it a tiny bit, but seeing how rare they are, you'd expect me to remember them), I've met one that wasn't in some way awful to be grouped with.
I have tried to be careful to speak only of my experiences and not moonkin overall, but maybe I slipped here or there. I have met non-terrible moonkin, just not in-game. So clearly there are some out there. Maybe I just attract terrible moonkin. I wonder if I will ever solve the Mystery of the Mean Moonkin. If you are a moonkin and not terrible, screenshots or you don't exist. :P