Tell your friend (s)he’s wrong. Your friend dislikes the new student out of jealousy and insecurity. Being nice and welcoming to the new student will make him/her feel better. He needs to fake it until he makes it, or else be seen as petty and jealous. Hopefully, if he can put on a front, eventually he will come around to actually wanting to include new people into your group. He needs a lesson regarding the golden rule. What if he was the new kid? Wouldn’t he want people to be welcoming? He needs to work on his empathy.