I'm fairly sure it's developing-feelings esque, but couldn't say for sure, or I could have that totally backwards and there's a former-lovers element. You see my dilemma? All I can distinctly remember is that Xander compare's Spike's shaved head to a mushroom in a simile, he refers to it as "compelling" [every time I read that line it makes me catch my breath], and I think there's something to do with Christmas. Maybe.
So there you have it. The compelling shaved head/mushroom simile story. That's the one I want. Go to it.