Rimming sugar?

I have a feeling this is somewhere in my bookmarks but cant find it.

Spike/Xander first time.  They may be roommates.

Spike acts weird after the other Scoobies leave their apartment and then sort of pounces Xander.  Turns out he saw the rimming sugar Xander had bought for Willow and Buffy's frou frou drinks and thought it was for rimming.  The sex was amazing so Xander just went with it.

Help?