You've got my empathy, too. Others have shared great tips, I will just add that when thinking of this...
In our case, DS says he can't stand up to anyone because he is immediately verbally attacked by three or four of their friends. It's a pretty common dynamic.
... you'd want to be sure that your child has a good grasp of where the line is drawn between standing up to someone, and saying something inappropriate which may cause
him to be seen as a bully/instigator/aggressor, and/or may escalate the situation. For example, making a personal attack or insult can be seen as verbal abuse (
ad hominem attack).
You may already be familiar with books which direct teach social cues and friendship... here is a brief roundup:
- direct teaching of
non-verbal cues- direct teaching of
friendship - direct teaching of
perspective taking- link to an article on the Davidson Database,
Tips For Parents: Gifted Children's Friendships-
post with roundup of articles on friendship
