My eldest daughter, she said 'shit' not so long ago and I noticed right away. I was like that's the first time you ever said shit around me. At that point it's a sign they trust you enough to be themselves around you. I know damn well they use those words when they're out cruising around or partying or doing what teens do. I'm not a moron.
Nobody wants their little ones to use the words. They don't do it right. They yell one word, it's always in public, and they repeat it over and over while laughing. That's still better than the kid who runs away every two minutes to go knock something over and won't listen to a damn thing their parents tell them though.