Hello and Thank You for using Just Answer. If you are religious, you can use the analogy with your grandson of how Jesus had long hair and he was a wonderful man. If your grandson believes in Santa, talk about how Santa has long hair and is in no way a thief. Explain to him how some people have short hair and others prefer longer hair...just like people their favorite toys. Ask him what does he think the boyfriend should do with his hair. If he replies, to cut it, then tell your grandson that it would still make him the same person. The more the boyfriend is around and interacts positively with your grandson, the better the relationship will become. Maybe your grandson saw a movie or tv show that had a long haired thief as one of the characters.
With regards XXXXX XXXXX piercing, he needs to be told that it is a way for people to decorate their bodies. You can discuss hair colors, tattoos, and then body piercing. First talk about how individuals get their ears pieced and others like to do the same in other body parts because they like the way it looks and we must be accepting of it. Tell him that even one day he may want long hair and a piercing. You never know!!
Hope this helps. If you need more advice, just ask!!! Have a good day!!!