We don't swear in front of DD or other kids, and we stress that swear words are disrespectful and very hurtful.
When she was four MIL thought it would be the height of amusement to teach her to yell "f..ing c...ts!" at the tv during the footy.
We only found out because she filmed it on her iphone and posted it on Facebook.
We started making a huge deal out of it. Everytime we heard it we'd say "How could you say that? You've hurt my feelings!" and go overboard pretending to cry. DD is a very sensitive kid when it comes to feelings so she'd start crying as well, and fling her arms around us wailing sorry over and over until she was forgiven.
It faded out after a very short time.
now if she hears a bad word she whispers it to me to check if it's a "feeling hurter"