If you prominently display a Confederate flag in whatever manner- like, say, hanging it up in your room or painting it on your guitar- as far as I'm concerned, you're supporting slavery. I don't know if it's the same as wearing plastic devil horns on your head or anything, but seriously... why would you even joke about it, just to look dangerous?
Why do you think they seceded in the first place? Isn't there a better way to show pride in your state in an edgy sort of manner without resorting to using a symbol of separatism?
I suppose I should talk, since I like skull and crossbones flags. But the original associations with them are long dead, and now we're more likely to associate it with Captain Jack Sparrow than real-life bloodthirsty thieves.