I am just teasing you guys, I know it's not "misunderstimate" with a "mis."
In my case, yes, people always underestimated my intelligence. I never understood why, since I was a good student and never felt dumb, but I eventually learned that "normal" people equate interpersonal abilities with intelligence, and since my interpersonal abilities were low (poor social skills, poor communication), it naturally followed that people perceived me as being unintelligent. I am more of a logical than an intuitive thinker, so it took me a while to grasp their reasoning...
Anyway, their taking me for an idiot motivated me to prove them wrong, which I accomplished not by learning interpersonal skills but by excelling in school. Did I succeed in proving them wrong? Sort of. Some people remained convinced that I was unintelligent, and attributed my academic success to my working my butt off (that was their conclusion); some others apparently rethought their definition of intelligence; and some others were baffled and coped with the dissonance by taking their negative emotions out on me: they bullied me, called me names, laughed in my face, etc.
Would my life have been better if people had accurately assessed my level of intelligence? I am not sure. I would have spared myself a lot of emotional pain, that's for sure, but at the same time I am not sure if I would have found the motivation to be a top student and eventually go to college. I just hope that there is light at the end of the tunnel and that my martyrdom will pay off some day.