I actually tell my kids to say the F word! It's been proven that when people swear, their pain level goes down. So at home, if my son hurts himself he's allowed to blurt out the F-bomb... his dad does it, and I'm sure he'd have started on his own eventually anyway, so he may as well reap the benefits of swearing now. He usually stops crying and starts giggling when he does it, so I guess it works! I tried to get DD to do it too, but she wont.
I'm surprised by some of the stuff in kids movies, but they learn all the words when they get to school or at parks anyway... I think it's better for their first exposure to at least some of the words be at home, where you can give an appropriate reaction to it. they understand the distinction between name calling and bad words fairly quickly. There are lots of words that are perfectly fine to use in the appropriate context, but are awful when used as an insult... for example, things that are broken, spoiled or used up are trash, people are not.