When I see this kind of thread, I am always surprised that some people seem to have been really traumatized by people who they describe as horrible DMs, and who they assume had really nefarious intents at some level. Once more, in more than 40 years of playing all over the globe, I have never met a really bad DM (in that sense, I had beginning DMs or people who were simply not as good as DMing as others, but no "bad" DM) - whereas I have met plenty of bad players (in the wangrod sense, if nothing else, and I know I've been one to some DMs - something that I really regret in retrospect, and that I have vowed a long time ago never to do again whatever the DM).
For me, it comes from the fact that being a DM requires preparing things for the pleasure of others, whereas a player can basically come to a table and expect to be personally entertained without any requirement on him whatsoever. It is by definition more selfless, as it is almost never about one's character (which, as a side note, is why DMPCs are usually a very bad idea).
Now, a DM's style might not be the right one for you, because he is directive, railroading, etc. But that does not make him a "bad" DM, just one that does not match your expectations. Just tell him "this game is not for me" and don't participate anymore, but calling him a bad DM behind is back is really not acceptable. Of course, the real adult thing would be to discuss playstyle with him, maybe he is simply a beginner who is unsure about his game, who has boisterous players much more experienced than himself and whom he does not know how to manage so that what he has prepared (however much incompetently, I'm sorry but we have all been beginners at some point in time) is not blown out of the window. And maybe something will come out of the discussion, maybe not (some people are full of themselves and their conviction), but at least the room will have been aired.
As for me, when I sit at a table, it's always with respect for the preparation that the DM has made, and trusting the DM that what he will do, he will do to entertain the players at his table, and he will do his best. And if necessary, I will help him (both as a player and as a character) along the way, because being disruptive is never going to help anyone have fun around the table. I will lower my expectations if need be, as a player or a character, I will make metagame decisions to steer my roleplay in the right decision if need be (the character is who I decide him to be, not something that exists in its own right). What I will not do is act like an entitled roleplayer and/or ruleslawyer who believes that he has any right to complain about what is happening in a game that I'm participating with (of course, there should be human behaviour limits and some behaviours should not be tolerated in games any more than in society, like harassment of any kind, but again I've never, EVER seen that).
And who knows, maybe it's through this attitude that I never had bad DMs, and that I've decided only once (I think, maybe another time) to stop participating in a game.
And honestly, the worse type of DM that has been described on forums is a railroading one (so what, there is almost always a bit of railroading in games, some published modules are actually worse than everything I've ever played through, and some players are happy with it) or one that does not recognise a pretend player's right to impose his own (view of the) rules or his build or his roleplay on the table - and for these, sorry, but the very rules of the game show that the player is wrong to do this, whatever the level - see "entitled player" above.
And when I DM, it's in full cooperative mode because there is trust all around, so I never have that kind of issue, and I am absolutely happy to give full reins to the players in terms of actions and description, because I know that they will not abuse that trust. And the other way around, they are absolutely happy to let me direct them where needed, even railroad if need be (although I play a very sandbox game in general), because they know that the intent is their own fun.