I'm going to have it out with my son's boss and all but drag him out of work
Seriously? Can you explain to me exactly why you want to have it out with your son's boss?
Because the boss is a hard arse.
It can be hard to have your son mistreated but it is not good to interfere in his workplace. You could put him in a situation where he could get fired and he will be upset.
Yeah but I'm going to tell him to get him fired. I'd rather have a bad son than a dead one.
Does your son even know that you are doing this? Do you think that he will understand your reasons? You could be upsetting him greatly, and losing his trust in you.