After re-reading this thread at random, and reading more posts since I last posted, I got a better perspective on what this thread is really asking. I answered a minute point to the OP, but now I will give a much better answer from my perspective. It is ultimately best to be yourself and not to hide your intelligence for the sake of hiding it. If you feel the crowd you're with will be threatened by it, or if you're afraid of this possibility and can't tell if they would disrespect you in a manner you could not handle, then your reaction is understandable. However, if you know others won't disregard you, you shouldn't specifically hide or not hide yourself to be a certain thing that is not you.
Also, keep in mind that some of these people who may be "dumb as rocks" to you may be excellent socially or in something else where you are "dumb as rocks."
Also, if you're a person who likes to correct everything, do your best to consider the emotions in the situation. (I know that's hard for many of us, but it's not impossible.) A person could be offended for you to correct something that might not be important, or not important to them. You could be seen as a "nagging mother".
With the mispronunciations, try not to get offended. Not everyone is good with language pronunciations. Just feel free to correct politely a million times. If they are doing it on purpose to annoy you, then that's a different story.