When children use bad words!

As parents we often use bad words during times of frustration, such as, being stuck in traffic, when our children(husbands) are getting on my nerves, when our car breaks down, if our favorite team loses etc. I could sit here all day and name a hundred things, but you get my point. So why is it when our children use them it's the worst thing in the world, and we always say to them, "where did you hear those words, don't ever let me hear you say that again" Why always the double standards with parents. I mean just because they are children doesn't mean they can't get frustrated, and show their emotions! Now correct me if I'm wrong, but do we, or do we not tell our children to use their words.