Xander and Spike in “Gone”

[as Xander walks in on Spike and invisible Buffy] Spike? What are you doing?

What am I-... What does it look like I'm doing, you nit? I'm exercising, aren't I? [starts doing "push-ups"]

Exercising? Naked? In bed?

A man shouldn't use immortality as an excuse to let himself go. You gotta be fit for killin'...

Ya-huh.