Keeping in mind that 'foul' language does not phase me one bit, it sounds like your son is being a
teenager. I don't think there's a need to panic and rush to a professional simply based on that. He's 18. During puberty, the body changes and hormones and chemicals are all over the place, and this is even more difficult for someone on the spectrum with consideration to our condition. It sounds like he got frustrated and unfortunately took it out on you. I do the same thing sometimes when I'm frustrated, it's kind of tourette's-ish. And I'm 45! Of course I have a lot more control over this now. But I do remember being that age, Lol. I can feel when my stress and frustration level is rising now and make adjustments.
I don't think you can prevent him swearing, he is technically an adult now, and will swear if he chooses. What you can make clear to him is that the insult hurt your feelings. That you don't wish him to use that sort of language around you. Make it clear to him but it sounds like something said in frustration, and I'm sure he didn't mean it. Sometimes things just come out.
What I would suggest is talking to your son, not from an angry or judgmental place, nor from a place of putting expectations of obedience. Treat him like a person. Tell him, without being overcharged with emotion, that what he said hurt your feelings. That as your mum, you feel you deserve to be treated with a little more respect (if that's how you feel, I don't mean to put words in your mouth, these are just examples). Be open about how it made you feel, but don't go overboard with authoritarian might, nor try to make him feel guilty or anything. Just be open and direct but not accusatory. Take a gentler tack. Try not to take it too personally. I know words hurt, but you are the elder, the mum, and I know it must hurt you a lot, and I am sorry for that. But, you're the one who is in the position to act with more maturity. Perhaps you might consider speaking to a counsellor for yourself, to explore why it hurt your feelings and affected you as much as it did. I say that with your best wishes in mind.
And a lot of us need support in our lives, that's why a lot of folk come here.
In adolescence, it is a time where people are coming into their own as individuals, on a psychological level, and of course there are many implications in this. It's a scary and confusing time, and is legendary for being a time where younger folk have a lot of intense emotions and this is happening while they are trying to establish their own identity and autonomy. I have seen and heard about many, many fights with parents in my lifetime. The only answer a lot of the time is to ride it out with as much grace and dignity as you can muster.
If he is engaging in true antisocial behaviour, such as purposefully hurting other people or engaging in violent behaviour, then I'd suggest counselling for him. If it's only episodes of swearing, I suggest it is 'growing pains'. Well, if he needs help with AS that is another matter. I wouldn't worry about counselling just on this one incident. Is what I'm trying to say.
But really, he's just being a normal teen (by 'normal', I don't mean ideal, I mean, that many act this way unfortunately, it isn't an anomaly). Many don't act like this, but a great deal do. You can fight it and that usually makes it worse, or you can be the bigger person and just ride it out. He likely wants to be his own person now and has his own opinions on things and you can't really expect him to be a perfect angel, he's an individual with his own personality. What you can make clear is that outbursts of insults are hurtful and not acceptable.
I wish you the best.
*edit- and by suggesting counselling for you, I meant in a way that it's ok for you to have someone to talk to and get support from. Sorry, I am aspie of course and sometimes people (especially NT folks) interpret my way of speaking in a less than positive light, which is my onus of course. But I mean what I say in positive terms.
