Hi OP, I have just re-read your OP, and my first reply to you. We now have a lot more information from your posts following your O.P. I was under the impression from your first post that your SS was the oldest of all your children, and your bio children were also your husband's bio children too. However, I am presuming that at least your child who is in Uni at the moment is not your husband's bio child, and is either the same age or older than your eldest SS? Do you share any bio children with your husband OP?
Some PP's since my last post to you have stated that this is not about SC, and whereas I agree that your eldest SS' behaviour last night, and your reaction to it, was what you were asking about, I am concerned for all of you that your and your husband's feelings, and treatments of each of your own step-children, is maybe what you and he should be considering.
Maybe if the bigger picture was more understood and acted upon by the both of you, the smaller picture may feel more understandable and more easily dealt with. It may even become the sort of thing that no-longer becomes an issue. From that I am led on to say that although it might be quite late in the day (considering the ages of the children we know about), do you think that some family guidance sessions could be helpful for you and your husband?
I say this as mum of several adult children, who have had a DSF for a large amount, to practically all, of their lives so far. He did not have any of his own (which I was disappointed about, mainly because I wanted him to be able to tell when he was not being fair to my children!). We stopped using contraception not long after our marriage, but sadly we never managed to have children together.
We went through some very tough times regarding the children, and even went to relate, which helped for a while. We have muddled through, and the child that my husband had the most trouble with - my eldest, he now gets on well with, but one of the others does not seem to like my husband as much as he did when he was a child, probably because they have very different characters, but they are both polite to each other when we meet up. My husband has always been closest with the youngest of my children, who has known my husband nearly all of his life.
I don't think that I am putting the issues I had with my DH on to you, but being human I suppose that I must be influenced by that in some way, and I do apologise if that has made me consider you more harshly than you deserve - but mainly you have my sympathy over your husband's differing behaviour between his bio children and yours. At this point I feel that I have to say please tell all the adult children not to drink any household alcohol without permission, not just your eldest SS, even though he is the only one you have an issue with. If your husband continues to not back you up where his bio children are concerned, then a visit to somewhere like relate may be necessary. I cannot stand children in a family set-up ever being treated differently to each other, and that includes my children's partners as well.
I don't think that you need anymore advice from any of us mnetters reading this thread, about how to handle your SS and his behaviour. Many other pp's have given you good advice/suggestions about how to handle your SS and your husband, and I also stand by what I said in my second paragraph. Good luck OP with sorting your husband out.