Why do people refuse to believe that I've read the Bible twice and Koran once, and can I sue them for...?

Do nothing. Whether he believes you or not is not the issue. Let him think you are a liar. Appearances mean nothing. And you could probably sue, but don't. It does nothing but hurt the community, and the lawyer would take most of the money anyway. Be the bigger man. (by the way, the more you tell people who call you a liar that "you don't have to believe it", the more they will believe you.)