i have a few faves. to list some:
*spike telling dru that the bird is dead and she freaks out
"sing birdie"
*the episode in s4 when the scoobies are all fighting (spike caused it) and giles is drunk, he is so funny when he goes to bed and then over hears tara is willows girlfriend "bloody hell"
that scene cracks me up"
*pretty much the entire episode when everyone forgets who they are (willows spell) anya keeps creating bunnies by accident, spike thinks his name is randy.
*buffy and harmony: H- buffy, we meet at last, B-weve met harmony you half wit
i love that one!
*spike and buffy: S- poor little lost lamb B- im lost? look at you, you idiot, poor spikey, cant be a man, cant be a vampire, where the hell do you fit in.
and much more, they are lots of funny ones.