We had someone else's cat staying with us and our three cats for a while. They never fought, but our oldest hated the "guest" and vice versa. I caught them once, one on a desk and the other on the chair, just loafed up and occasionally growling and hissing at each other. I have no idea how they ended up together, but neither of them wanted to move. It was pretty funny to watch.
We have Bunny(11) and Korra (3); Bunny hates Korra and they’ve lived together since Korra moved in at 8 months. Korra just wants to play and snuggle, Bunny ain’t got no time for that.
That's what's hilarious to me... we brought Lorelai in at about 6 weeks, Rocket hated her instantly with the power of 1,000 suns, but our 3rd cat, Keanu, loves her. They are best buds.
But when we got Keanu and he was a baby and Rocket was 2, it was the exact same reaction.