It all happened because Xander decided to do some spring cleaning.
Now, anyone who knows Xander could tell you that this is an extremely rare occurrence, but these were special circumstances. There were still about six boxes of stuff he'd never unpacked from his move to the new apartment, and since Anya had left him, a couple of weeks before, he had a bit more time to himself. He finally got so fed up with dodging the boxes every time he tried to go to the bathroom that he decided to just unpack them, and maybe get some cleaning done while he was at it.
This turned out, against all odds, to be a fairly momentous occasion.
Not that anyone knew this at first, of course. At first they were just surprised. Xander, cleaning? Whoever heard of such a thing? But they all shrugged, and Willow made a joke or two, and Anya, who, against all the other odds, had still managed to remain friends with him after their tumultuous breakup, came over to help him with his cleaning.
It turned out to be a momentous occasion because of one very important thing: when Xander was unpacking, he discovered his old, battered copy of The Hitchhiker's Guide to the Galaxy.
Xander was, of course, delighted. The Hitchhiker's Guide to the Galaxy had been one of his favorite books in his early teen years, before Buffy had come along and his world had been turned upside down. Not long after that momentous day, he'd set the book aside, along with the equally battered copies of The Restaurant at the End of the Universe; Life, the Universe, and Everything; So Long, and Thanks for All the Fish; and Mostly Harmless. These books had not seen the light of day since, and it was purely by chance that he unpacked them on this particular day.
Of course, anyone who has actually read these books can tell you that there are a great many things in the universe that only appear to happen purely by chance, and in fact have some greater and much more interesting purpose to them, but we'll get to that later.
On this particular day he was cleaning and unpacking alone, without Anya's help, and so he had no reason to not sit down immediately and start reading them all over again. This, as you will see very shortly, was the beginning of something that was really quite astounding.
You see Xander, being the funny guy that he is, is not the sort of person who can let humor pass him by without sharing his appreciation of it. Therefore, he promptly began to share all the humor from these, his favorite books, with all of his friends.
Unfortunately, his friends had absolutely no clue what he was talking about. None of them, including Giles (who really should have been at least vaguely exposed to one of the most fantastic things to ever leave the shores of Britain, and I do mean including tea), had ever read the books. So, if, for example, Buffy teasingly pointed out that Giles looked somewhat hungover, and Anya then pointed out in her typical blunt fashion that Giles had consumed entirely too much scotch the night before, Xander found himself unable to resist making a comment about a Pan Galactic Gargle Blaster. And all of them would immediately look at him with the most confused expressions Xander had ever seen since Giles had once suggested to Buffy that perhaps she should not go out slaying when wearing her brand new strappy high heels.
Now, the one single fact that makes this entire story more than just another meaningless narrative is the fact that Spike had, in fact, read The Hitchhiker's Guide to the Galaxy.
Therefore, Spike actually understood all of the jokes Xander made. If Xander made a reference to a Hooloovoo, which is, of course, a hyper-intelligent shade of blue, or to the number forty-two, or even anything related to Deep Thought, mice, Vogons, improbability factors, the Heart of Gold, manic-depressed Robots, and innocent sperm whales, Spike knew exactly what he was talking about.
This is important for two reasons. The first reason is because it annoyed everyone else, Buffy most especially, that Spike knew what Xander was talking about and she didn't, and annoying the Scooby gang was something that Spike enjoyed above anything else. And everyone wants Spike to enjoy himself, correct?
Well, everyone besides Buffy. However, this not being the point, I shall continue to the second reason.
The second reason is that the abundance of Hitchhiker's Guide humor had the simple and profound effect of bringing Spike and Xander closer together. Entirely mutual hatred was forgotten in the face of the fact that they now had inside jokes.
Anyone who has not observed the power of inside jokes should not be reading this, because not only are you too stupid to observe said power, you probably should have skipped this over when you saw the title. Everyone else will understand what I'm talking about, so I won't bother to explain.
It didn't take long before the two of them became actual friends. More surprisingly, to both themselves and anyone who'd ever met either of them, they became close friends. Xander found himself spending more time with Spike than he did with the others, and both of them were, against all of the odds that weren't already mentioned, deeply surprised about this but happy nevertheless.
The moment when things became even odder for both members of our intrepid duo occurred when, as these things tend occur, they both got blindingly drunk, and ended up having sex on the floor next to the couch.
Now, one would think that when both of them woke up the next morning, one or both of them would be worried about the consequences of what they had just done. They were mortal-enemies-turned-best-friends after all, and that can be an unsettling mixture to add sex on top of, especially if one had been blindingly drunk the night before.
However, neither of them had any sort of predictable reaction to the sudden realization that mere hours before they had suddenly become much closer than ever before. Instead, Xander, who woke first, sat up rather slowly and creakingly, and said, in a somewhat hoarse voice, "Why are on the floor next to the couch?"
"Good question," said Spike, who had woken up when Xander spoke. "Though I don't see what it has to do with anything."
"Well, if we were so determined to have sex-"
"And we definitely were," Spike interrupted with a somewhat toothy smile. Not that toothy smile, mind you- just a normal human toothy smile.
"Then you'd think we'd have at least made it to the couch," Xander continued doggedly.
Spike shrugged, supremely unconcerned at this idea. "Doesn't matter much one way or the other, does it, mate?"
"Not really," admitted Xander. "I was just wondering."
"Well, wonder about something else," Spike told him. "Later."
Then Spike kissed him, and things took their natural course once again. Possibly twice or thrice again, but who's counting?
The upshot of this tale is to demonstrate the fact that you can never predict what will happen. An innocent unpacked box led somewhat surprisingly to a romance that has been described as the oddest in history by the sort of people who know what they're talking about. There are strange and mysterious forces at work in our universe, and all that anyone can say about them is this:
Have you done your spring cleaning this year?