There can be no pen and paper roleplaying game without a game master. This is a dictum that, aside from a few games (that I would classify as collective story telling and not games at all), has held true throughout time. Players, you need to trust your game master. There's no game without him; he needs the leeway to make the game function and shouldn't be hamstrung by your trust issues.
That having been said, game master: you must be worthy of trust. I've addressed the poisonous Player's Rights movement that has informed so many of the modern pen and paper rules, but so far I've not actually spoken about the key issue that lies at the very root: the lack of trust between player and game-master that so permeates modern roleplaying games. Where does this lack of trust stem from? It is most likely not a flaw on the part of players, to be fair. So who do we have to blame for this virulent movement? Why, none other than the abusive GMs that put the fear into people so badly that they felt they had to design rules to protect themselves!
Luckily, there are ways to tell if you're an abusive GM; you can change, I promise, and you won't even have to have a player-held intervention.*
Signs of abusive GMing include, but are not limited to:
Grudge monsters. If your players make you angry so you force them into a scenario where they are in mortal danger as a punishment, you need to reexamine yourself immediately. It may be time to completely surrender the GM screen and let someone else run the game. This kind of behavior, more than anything, leads to players feeling violated.
Dice fudging. It's fine to do as long as your players don't find out, right? Well, while you may be inclined to protect them by fudging dice in their favor (admirable) or make the situation more dramatic by fudging dice against them (diabolic), there is no surer way to undermine the player's confidence in your impartiality. If they cannot trust the dice, they cannot trust you.
Shifting goalposts. Don't change the rules to suddenly favor someone or some other tactic (PC or NPC). If you're going to alter your rules, make sure you have a discussion with all the players before a session begins (or even in-session if you suddenly find something unpalatable). Do not just haul off and change the rules without consulting everyone. That makes for angry players.
Glory hogging. Don't become attached to your NPCs in the same way a PC is attached to their own character. If you're impartial, it's ok to let your NPCs do a lot. I just recently had an NPC save the entire PC party from destruction (at the hands of another PC no less, perhaps the story will follow). Mike at Really Bad Eggs talks about something similar here.
Breaking the rules. The rules of the game are a contract. You sign that contract with your players, and they expect you to abide by them. Similar to shifting goalposts, above, this one is even worse. At least there you might be trying to remedy some flaw inherent in the rule system. BREAKING the rules for your NPCs is just filthy. If you do this, you ought to be ashamed.
Railroading. Whether by means of illusionism (see the Quantum Ogre) or some other method, if a game is meant to have a sandbox environment (like D&D), forcing the players down a specific path will surely make them hate you. This obviously doesn't really hold true for games like CoC (ignore the predesigned adventure? The world ends!) but it has very important ramifications for games that are meant to allow freedom. This is most often the abuse of a GM who doesn't hate their players or want some kind of power kick (unlike most of the breaches above) but rather someone who really LOVES their players and their game and wants to see the best story possible told. Guess what? The best story is one that makes itself, not whatever dimestore pennydreadful you want to trot your friends through. If you have the urge to do this, stop and write a novel instead.
Playing favorites. An even more dangerous version of dice fudging and breaking the rules, this is when it affects one or more members of the party but not everyone else. While dice fudging can be done with good intentions, playing favorites is just a blatant breach of even the most basic agreement of trust that your group has with you. Don't you do it!
If there are any more signs that anyone can think of that highlight abusive game-mastering, I'll be glad to discuss them and perhaps add them to my list.
*imperative to note that none of these apply to Paranoia, in which you are expected to be abusive.