Don't give up yet. This is getting to be a pretty interesting game. If it isn't any of the above mentioned stories then it might be this one of my old favorites: BLUE -- by: Pandora.http://spikeluver.com/SpuffyRealm/viewstory.php?sid=31753&warning=NC-17
Spike is a college professor but she doesn't know that in the beginning. They meet in a bar after Spike spills a drink on her. Faith works there. A little later in the story, they meet again in a store. Buffy and Spike are both after the same brand of cookies. Then the store gets robbed and Buffy gets her knee hurt. Spike takes her back to his apartment to fix it.
Does that ring any bells? I hope you find the one you want this request is driving us all crazy too.