I like pretending not to be American.
Why do you pretend not to be American?
So people don't think I'm an idiot.
Your nationality has nothing to do with your intelligence. You don't have to lie about it.
I feel like it's a political statement about my dislike for American politics.
Rather than lying, you should work to create political change. Then people will  see you as someone intelligent who does something about things that go against your beliefs.