I've been a fan of many different things over the years and there are patterns to fandom that occur regardless of whether it's computers or tv shows. The patterns are a simple combination of human nature and the close knit nature of most fandoms.
We Think We're Special
One of the most irritating habits that fans have is a tendency towards self congratulation. Since we all like this special show and other people don't we must be special, right? No, not really, we just happen to be a little obsessive about a tv show. It's harmless, but it hardly makes us special.
The problem is it's a very short trip from patting yourself on the back to looking down on everyone else and then it's all downhill from there.
We Think They Owe Us
I see this one a lot. The assumption that since we watch the show and buy the merchandise, the creators and actors are somehow beholden to us. That they owe us their time and that they should do what we want. Nope. It's a very simple exchange. If you like the product buy it. If you don't like it don't buy it. Really it is that simple.
It's nice that between the internet and conventions we have more direct access to the writers and actors, and it's nice that they often do take time to listen to what we have to say, but that doesn't mean we are entitled to it.
Obsessive Continuity Disorder
As they get more invested in a show, fans have an unfortunate tendency to get obsessive about the details. Stuff that really doesn't matter very much. Comics fans are some of the worst. Honestly is it really significant if the latest Spider-man story contradicts something written in 1972?
Yes those little nods to the fans are nice to see in movies, but little nods is all they should be. As soon as they start to dominate the storytelling everything falls apart.
Guardian of the Character
I've lost count of the number of times I've read complaints that a character wouldn't do that or wouldn't say that. The fan sets himself up as the guardian of the character. The problem with this even a most cursory exploration into how people react in real life will show you that there is no way you can make these statements with absolute certainty. History is full of examples of people acting "out of character" in unusual circumstances.
Zero Business Experience
I've lost count of the number of times I've heard arguments from fans about how they would do things better if they were in charge. Doesn't matter if it's comic books, tv or movies. Everyone is a backseat driver.
The problem is that nine times out of ten they don't know what they're talk about. Criticizing the Editor in Chief for a business decision doesn't make sense, that's not something they have control over. Expecting a network to keep showing a tv show that has low ratings isn't reasonable. Wanting a show's running time to be increased when it's budget has been cut isn't reasonable.