Have someone first expression of you been really wrong?

People that meets me for the first time thinks that I'm the quiet/lonely type that likes reading and is extremely nice and smart and someone that obeys every rule.

But in reality
I'm not that quiet and I have a lot of friends,
I can be nice only to people who deserve it, if you don't then I won't be
I am known for being extremely mean
I can be a trouble maker and I love fighting