Talking to them probably isn't quite the most effective approach. The way to zap them out of their malaise is to raise your hand in class and ask a deeper question on the topic at hand that they are trying to "teach" you.
The thing is, you have to be persistent. If they are already talking down to you, then they will not give you a deep, satisfying answer - they will just give you a simplified answer. Then you will have to go back and question their answer and explain how it doesn't cover what you're really thinking, and fight any attempts to wrangle the conversation away from you and back to their Magic Outline/Program of Doom.
This is very difficult to do, so don't feel bad if you don't get what you want the first few tries. The problem with these people is that they think you are less intelligent than you are, so you have to show them that you already know what they are talking about and want to get deeper with them. (To be honest, I haven't done this enough over the years, heh.)
If you can, you should also get any of your friends in on this too, so that the teacher knows that the group intelligence is higher than he or she originally thought.
You can also say, "I already understand what your saying here," but the problem with that is that it leaves the teacher and you stuck and the conversation nowhere to go.
