Rule number (insert HIGH number here) in your adult life should be this:
Don't swear in front of your kids or your parents.

I don't care if you're out having fun with the guys and you wanna drop a few "F" bombs. Go for it.
God/Muhammed/Zeus isn't going to strike you down and it's a good way to let off a little steam.
Just keep it where it belongs. If a mom and her kids walk by, zip it. If you don't notice until it's too late, APOLOGIZE!

You'd be surprised at the reaction from most parents if you apologize after swearing in front of their kids.
They're likely to see you as a good person instead of the asshole pedophile they saw you as only moments before. You may think you don't care, but the good feeling you'll get afterward will be worth it's weight in gold.

Swearing in front of kids does two things. It teaches them that swearing is acceptable language and it lowers their expectations of you. As a father/mother you should never lower your kid's expectations. And handicapping them by teaching them that swearing in mixed company is OK will only cause them to have trouble later in life.

Swearing in front of parents (and sometimes bosses) brings you down a few knotches on the respect ladder too. It tells them that you don't really respect them enough to use your manners around them. It also shows how poorly they raised you. Even if they did a smash bang job they'll still think of you as a plumber instead of a doctor, regardless of your profession.