[Buffy doesn't flinch or move when Spike leans into the stake a bit. She believes his bravado, knows Spike well enough to know (or she thinks she does) how far he'll push it. This is the same vampire who let her nearly beat him to death once (or it would have been death if he hadn't already been dead).
She doesn't say anything, because there's nothing to say. He's got a point and she knows it. She presses the stake a bit harder into his chest, her expression going hard and cold. It's the evidence of the last several years showing itself on her face. For one moment, that one moment, she's all slayer, no girl. All General.]
I'm not that eighteen year old girl you know anymore.
[and she steps back so suddenly, withdrawing the stake with slayer like reflexes.]