Let's get one thing straight -- when Mimi swats me on the head, I swat her right back. And when she whacks Farfel, he whacks her right back. Just because she's a girl, she doesn't get special treatment. She can dish it out, and she can take it.
That's the way it is with cats. A smack in the face equals a smack in the face back.
But we only let the fur fly for so long. It's infinitely more enjoyable to play. Or sleep, or eat, or clean behind our ears. Farfel especially likes to clean Mimi's ears, even if she's been beating up on him.
Because as Abraham Lincoln observed, "no matter how much cats fight, there always seem to be plenty of kittens."