I’ve only come to this thread as it’s still showing in GC and that it’s been moved here.
I swear occasionally, usually when doing DIY and something goes awry - it’s an expletive, and an outlet of frustration.
I never swear in conversation - unless telling a story that involves a swear word, and then usually replace the word with something like ‘fudge’, or whatever. Actually, that’s not quite true, as occasionally at work I might, to my colleagues, say something like ‘fudgety fudge fudge fudge’ (replace as appropriate), if something outside of our control has just delayed us and we can’t do anything about it - but it’s said in a jocular banter sort of way, simply to express frustration in a humorous manner.
I guess I’m a bit ‘James May’, in that I’ll say things like ‘cock’, when of course we all know I mean something much stronger!
I was once told by a teacher that we swear when we’ve reached the limit of our conversational ability, and that it’s the product of a limited education. That if we all learned, and embraced the English language to it‘s fullest, we would have no need to swear.
In day to day conversation, I’d have to say I agree (to an extent), we simply can’t be bothered, or lack the vocabulary, to give long descriptions of something, or someone - it’s simply easier to call them/it ’a fudgeing prick!’ than go into the why‘s and wherefore’s of what has irritated you. So swearing can be a product of a limited education, although I’d say for the most part, it’s a product of being lazy - a shorthand if you will, when we simply can’t be arsed to explain exactly what we mean, and everyone will get the ‘spirit’ of what we mean if not the real nitty gritty.
And then there are peer groups. In some groups it’s almost expected that swearing dropped casually into conversation should be the norm; indeed, you can almost feel pressured to speak in the same way, just to gain acceptance from your peers. Frankly though, it’s a poor decision to do this, as everyone sinks to the lowest common denominator, and it becomes self perpetuating. If you don’t swear, you can be seen as ‘precious’, or trying to put yourself above others - a totally perverse situation, but one that certainly exists in many places.
My mum was a headmistress, and there was no way I was allowed to swear in the house. To this day I would never swear in front of my mum, and I’m in my mid fifties now!
All the way back to the OP, it really depends. I wouldn’t expect my lad to swear in front of me, and I’d have words if he did. Doing DIY is different, if he swore as an expletive, skinning his knuckles when a spanner slips, I reckon that’s fair game.
In casual conversation, or online, or wherever, absolutely not, not in my house! The same rules apply to anyone in the house, I wouldn’t have friends over and expect them to swear in front of me, or his friends, or tradesmen, or whoever. He’s 18 now, and an adult in his own right, he can make his own decisions, but he know the consequences of breaking the ‘house rules’.
Personally, I’d be having words with the lad, (they don’t have to be stern, unless he pushes back) he’s living under your roof, and should be abiding by the rules of the house, whatever they may be. Of course it’s easier to let it slide, giving guidance to others as they approach adulthood isn‘t always easy, as they are forming their own opinions (and of course know everything at this sort of age)!
Everyone is different, but it wouldn‘t, and doesn’t, happen here.