Is blackface always offensive?

[Shell B]

I think racist jokes are fine, as long as the butt of the joke is the racist. Like, if you were to don blackface to make fun of the people who donned blackface in order to insult black people. I honestly say racial slurs all the time, but the joke isn't on the race in question. I'm laughing at how ridiculous the joke sounds. I don't know if I'm explaining that right, but there it is.