Why do bullies complain when you bully them back?

I'm usually a cordial and respectful guy in my daily life. But if someone is being awful, rude, and disrespectful to me, I'll give them a piece of my mind and dish it back to them. The thing I find hilarious is the very people who were terrible to you will start whining that you're actually the bully when you're just dishing their behavior back to them. Are they just unaware of how they're coming across? Just curious.