Sometimes when a cat grooms another cat, it’s nice. A cat helping another cat out, cleaning those hard-to-get spots on the back of the neck with a friendly lick.
Other times? It’s more like, “Hey, I want that nice nap spot, and I’m going to annoy you until you give it to me.”
My cats exclusively bathe each other to initiate kitty cat combat. “I’m bored, do you want to play?” I tried it on my wife and it initiated combat in that context too.