They called me a liar in 2012 and I don't fully forgive them!
It's sad that you are holding on to something from so long ago. Why can't you fully forgive what was said?
Because they lied to my face.
It's wrong to lie under any circumstances. Nobody is going to trust them if they know that they have lied.
They made fun of me and other people too.
Holding on to a comment that was made about you will only continue to hurt you and cause you to reflect on yourself in a negative way. Forgive the person and let go of the comment instead of carrying it around like a label. This will help you to heal and move past it for your own sake.