Have you ever seen a group of cats together? They roll around play fight, they butt heads to say hello and they groom each other. This behavior spreads the scent around and each cat then smells like the group. It gives them a sense of belonging.
When I brought the stray who became “Buddy” into my home there was the usual spitting and hissing but eventually Buddy worked his way into the group. He and Rocky roll around play fighting and race around the house . 
They groom each other. Smokey will have no part of it and in the beginning I actually saw him acting like a prey animal, slinking away to hide under the couch. This made me very sad.
As time has gone on Smokey has gained more confidence around Buddy but he still won’t groom him or let himself be groomed. Rocky can groom both Smokey and Buddy and both will groom Rocky but Smokey gives Buddy a wide berth.
About a week ago things began to get interesting. Buddy came bouncing over to me meowing persistently. Now Rocky is the vocal cat, Buddy gives me little chirps and “merps” and Smokey just purrs so this was a little out of character. Clearly something had Buddy upset. At first I didn’t see anything to cause his distress but then my eyes went to the cat tree.
Rocky was stretched out under his heat lamp but Smokey was not on his usual perch. No Smokey was in the “Crow’s nest” at the very top. From the first day Buddy joined us this has been his place. And here was his sworn enemy sitting in his special place.
To make matters worse Smokey couldn’t get down. He start and his clawless paws would slip so he’d back off. I helped the miscreant down and Buddy climbed up and all was peaceful again.
A couple of days later I got a visit from a very agitated Rocky. In actions very reminiscent of Buddy, Rocky was meowing and pacing until I got up and followed him to…the cat tree. There, under his heat lamp was Smokey.
Rocky would stretch up and nose him and all Smokey would do is turn around and show him his butt. I had to laugh. As I stood there Rocky got up on the perch too and unceremoniously pushed Smokey off. I guess he just wanted “Back up”.
Poor Smokey. Buddy came over , ears up, whiskers forward, just being friendly and Smokey would have none of it. He flattened his ears and whacked Buddy’s nose with his clawless paws and stalked off. Ok Smokey. Clearly you have not learned to play well with others. I think we’ll just have to call you Mr. Crankypants from now on.