Bullying at school

Last week, my 14-year old son was pushed to the ground by a classmate. He's had serious problems with being bullied in the past (he's your classic easy pick; scrawny little nerd with glasses), so like I always do, I called the school and gave them a piece of my mind. The principal was very compassionate and said she would get to the bottom of it. Well, today I found out that my son was pushed because he called the other child a fat A**!!!!! MY SON????? The one whose mom is currently 330 lbs and scheduled for RNY on Novembe 2nd? How ridiculous! Anyway, I gave him the mother of all lectures....I hope I made him understand that this scars a person for life. I also gave him a crash course on my upcoming surgery and that this issue is nothing to make light of. It brought him to tears, so I hope I got through. Any thoughts on teaching them compassion without scaring them?