I just love the one in s7 where she goes all :
- Buffy: you...you are dope!...
- Spike: wait what?
- Buffy: YOu are dope and bonehead and *thinks for a second what so say* and you are shirty!
- Spike: Have you gone completely carrot-top?
It just rings back so much to the spike's line's few seasons earlier(even delivery and reactions are identical):
- Spike: and and, I never really liked you anyway and... and you have stupid hair!
- Buffy: *what-face*
AS for overall:
My favorite spuffy moment: every damn one of them to have ever exist lol.