[as Xander walks in on Spike and invisible Buffy] "Spike? What are you doing?"- Xander
"What am I-... What does it look like I'm doing, you nit? I'm exercising, aren't I?"- Spike
[starts doing "push-ups"]
"Exercising? Naked? In bed?"- Xander
"A man shouldn't use immortality as an excuse to let himself go. You gotta keep fit for killing."- Spike
"Ya-huh."- Xander