In my home, the only "bad words" are the ones meant to inflict pain on other people. I don't care about the f word if my daughter stubs her toe and it hurts! Yell whatever you have to if it helps you deal with it! But God help her if she ever called somebody stupid, ugly, retarded, fat or any other cruel word meant to harm another person emotionally. That has always been the rule in my home....the only bad words are the ones that hurt.
Now, as far as the words society has declared "bad" I have always allowed her to use them with two exceptions. She may not use them just for the sake of it. That is annoying. Any word use excessively or just to sound tough is annoying! And she may not use them in public or around people who may be offended. In other words, use common sense and respect that not everybody is comfortable with such language. Other than that, in my opinion, they are just regular vocabulary words. Nobody is gonna tell me there is a difference between "darn" and "d**n." They convey the same meaning, yet one is considered "bad" and the other people are perfectly ok letting their kids say. Makes no sense to me at all.