I remember being just as shocked when I read it! I think Spike was mean to Buffy, because he has every right to do his own business but why do it at her party? under her eyes? you can see in that pic that she's disappointed and angry at the same time and I agree that she made a fool of herself, getting drunk and with Riley, in reaction to that. On the other hand I didn't like her being mean with him as well. Spike wasn't stalking her, he wasn't hiding or else so why call him stalky? and why clown?
But go on reading! they will talk again of 'that night'