Does anybody know any good bible verses on being hypocritical, gossiping or how a mentor is suppose to be?

I have a friend who is basically getting kicked out of his friends apartment because they have a grudge with his brother and is being totally hypocritical in the situation. He is gossiping and talking behind his back and had a "POW wow" with all the other guys living in the apartment except him... it just seems really hypocritical because this "friend" is also suppose to be a mentor. I just would like to know if there are any good verses on how a mentor is suppose to be, gossiping, and or being hypocritical? Thank you!