I'm a better english speaker than my english teacher
Why do you think that your English is better than that of a teacher?
I think I speak better than that old illiterate bitch
Your teacher is a professional, you should not be so rude about it. It is good to feel confident in your abilities but also keep a level head.
I think I might make a better teacher than that old bitch.
Well, right off the bat, I can see that you ordered your adjectives incorrectly, and you should have said "illiterate old bitch" so perhaps your English isn't as strong as you would like to believe.  The much bigger issue, however, is that you should never say something so disrespectful of a teacher, even if you don't think she is very competent.  You need to pass your classes in order to move on in life.