Not exactly the Queen's English

I was in the kitchen with Hannah making Rice Krispie treats, and she did something marginally inconvenient, from which I redirected her.

Hannah: Oh, sorry, my fault.
Me: Excuse me?
Hannah: I said 'my fault.'
Me: I know it's your fault, that's why I asked you not to do it.
Hannah: *blank look*
Me: Do me a favor and don't say that any more.  Don't ever say 'My fault,' or 'My bad.'
Hannah: Why? What does 'My bad' mean?
Me: It means 'I'm a dope, and I don't know how to say I'm sorry.'  It just doesn't sound very intelligent.

I know there's no way to keep slang out of her vocabulary permanently.  I use slang.  I call her Dude all the time.  Sometimes I end sentences with 'yo,' albeit mostly when talking to my sister.  I'm not all that bothered by her frequent use of the word 'totally.'  But street slang is just gross coming out of my sweet little popkin in her polka-dotted skirt.