Your son needs to end all conversations with these people, unless it pertains to his doing his job. If they try to begin any type of personal conversation with him, have him walk away, leave the area. I don't know where he is stationed...on a ship? Home port? He doesn't have to engage in simple talk with simple people. He can just ignore them and walk away, or have him tell them to please leave him alone. Trying to reason with Liberals never gets anyone anywhere. It's frustrating and it's useless. Better to ignore them and pretend they don't exist. Liberals hate that more than anything.
There's always going to be a$$holes no matter where he works. You just need to learn how to avoid them and ignore them. None of them are worth giving up a career over.
I also recommend that he not have any personal items that they can get their hands on. If he has any way of locking these items away when he can't be in direct control of the stuff, he should do it.
M55th nailed it. He has to just let it go. It may or may not be fruitful to tell the jacka$$es that they can "agree to disagree" and "let's try to just get the job done together"; I don't know. He may even be able offer to buy 'em a beer, but I suspect it has gone beyond that. He's an E5, and I suspect they are 2's or 3's, possibly a 4 thrown in. The jerk who got in his face may be scrapping for a fight anyway, so who knows if that conflict can be defused - it all depends on what these people are like. Coffee cups are no big deal, but he neads to find a way to drop all of this and keep it from escalating, both for the sake of the unit and for his safety. Accidents happen aboard ship. If he cannot find a way to keep the peace while while in discussions he should avoid those topics. They may try to bait him, he needs to show them they can't get to him. Stick to business, be fair, do the job. Hopefully this will blow over in short order.
If these people are 6s or greater then he needs to pull his head out of his hind quarters. While I doubt this is the case, In the Nav I knew, if your 1-PO and especially your CPO had an axe to grind to the point of being "in your face" - you were in a world o' hurt. They have the power to dispense scads of crap, in most cases with the full sanction of the command, and the know-how to make one's lfe miserable. As a PO2 he likely isn't to that level of authority or experience yet. When will he make 1st?
Lastly, he needs to relax, and so do you. There is no shortage of people like them, and he will be working around them for the rest of his life no matter where he goes.