It's an old story, I think. Basically, it happened during the Olaf episode, or maybe the story simply added it. I don't remember. What I do remember, is that Spike sent Xander to get reinforcements, and when they came back they were gobsmacked to see Spike and Olaf sitting at a table, having a relatively deep conversation (although I think Spike was doing the talking really), whilst eating onion rings and spicy wings or something.