The Tourette's joke offends me. (I have a nephew with Tourette's and can assure you that the popular culture description is way off.) When I read Charles' reply, I mentally bet myself that you'd reply the way you did, because I made a similar joke a long time ago. (And I can see where it would offend some)
My brother was diagnosed with a form of Tourette's when he was a kid, and I did a research paper on it in college. I won't claim to be an expert, but I probably know more than the average person (and I'm sure you probably know more than the average person as well).
The swearing occurs in maybe 10-15% of cases. My brother was definitely in the 10-15% - sadly, he was treated cruelly and even viciously by adults who thought his concatenation of swear words was just bad behavior (which only made the matter worse).
But anyway, while I realize it's not something to laugh at, the point is that involuntary swearing (coprolalia) does occur - it''s not as common as the tics and other symptoms, but is certainly the one that gets the most cultural attention.
More people are being diagnosed with Tourette's now than maybe 20 years ago, because (not unlike autism) the classification has broadened.