When I go to pick my 12-year old AS son up from school, I see how rude the other kids are. I'll be walking to the school, with my 8 year old, and these middle-schoolers are sauntering along shouting vulgarities at each other, spitting, swearing. I shudder to think what they are like when they are not passing a grown-up with a child.
My son is not like that, although when he's having a meltdown he uses the f-word. He didn't use to, but he hears it at school so much, it just happens. I disapprove, but mostly let it slide, provided he's really in a meltdown. That's what those words are for, I suppose, and it's better for him to blurt out a few harmless words than to than to throw a chair at his brother.
The only time he's rude, pretty much, is when he talks about inappropriate things while people are eating. "Doesn't this food look like it came out of someone's nostrils?" If people get angry or annoyed when he does that, it sends him into silly-mode, and he seems to be unable to stop. It's like he goes into another zone, and has to get it out of his system before achieving normality.