Can't say I agree to be honest
Children (including my own) go through some of the most awful bullying at school. Leading to self harming, long standing MH issues and in extreme cases suicide. It is not ok in any walk of life to bully. If this is man was called that at school... then that is bullying.
I imagine for any adult who has gone through school life being bullied to have that brought into their adult life would only bring back the most awful of memories. If it's not true then it is still bullying no different to a lie being said about anybody in their past life which would bring embarrassment.
When you see the outcome of bullying to the affect it had one of my children you may not find it so funny. I presume this man has a different political opinion and therefore it is ok to laugh and make jokes. Same as a racist wouldn't crack jokes about someone with the same colour skin of them but would make fun of the opposite.