After a few hundred years of fighting for dominance, the sparring of your partner becomes terribly predictable, and what is a mere century to a vampire's muscle memory? Spike still remembers the way Angel's body would move around his, the way he would typically hint at the left only to go for a quick right.
Spike goes blindly for Angel's right jab without even waiting for the left to fall, and then he almost as automatically goes for a knee in the nuts. He never did win over Angelus by fighting fair. But Angel's memory serves him just as well, and he puts a leg out to stop the intrusion. Spike holds an elbow up to meet the fist going for his head. It's like a carefully coordinated dance, which it took them forever to develop, but for all its intricacy they remember it perfectly and they dance it well. Spike knows he'll have to come up with something new, anything to surprise, if he is to even have a chance to win. Of course Angel knows this just as well, but in the years that have passed since last they fought each other neither of them has had any reason to learn anything new. With someone who doesn't know their heads inside and out, nothing more is required. So the dance goes on.
Eventually they're both too tired to continue and the fight becomes less about trying to throw the opponent through the wall and more into at least getting him to fall to his knees. It ebbs out into a pathetic sort of wrestling before long, just the two of them grunting together, even the tempo of their breaths in perfect sync. Too bad, Spike thinks, that they can't hunt together anymore. Hunting with Angelus was like hunting with an extension of himself, especially at the end. Once Spike was fully grown into his role as a vampire, the two of them was a force to be reckoned with. And if it hadn't been for the women...
Angel interrupts his train of thought.
"Just like old times, huh," he pants.
"Yeah," Spike agrees. "You haven't learned a single move since the 18th century."
"Why change a winning concept."
"It's not winning now."
Angel laughs and Spike joins in, and before either of them knows it, they collapse together on the floor, laughing and laughing like mad. Spike is glad this fight wasn't serious, wasn't about anything other than getting some anger and frustration out, but somewhere deep inside something is nagging at him. He almost wishes this had had a purpose; a purpose to justify the whole thing, something to give it a little sense of... meaning. In the past, there was never any need for a meaning.
"I miss it, you know," Angel says so quietly Spike for a moment thinks he's imagined it. It sounds suspiciously much like a confession and Spike will have no part of it. If Angel wants to be a cry-baby, fine, but Spike sure as hell won't. Spike will go out and find the next big thing, with or without him. So he rises and walks out, calling a casual "later" as he saunters out into the night. God, he needs a fag.