The instant he tapped her chest she thought herself lucky that she didn't topple over. Feeling a little weak on her feet? Yes. But not in the knees. There wasn't any kind of amorous feeling going on here. Just anger and shock.
Buffy thought she'd already suffered all of her blows when it came to the fun game of, 'hey, you've conveniently missed out on several years of your life, aaaand this is what you don't know!' In fact, she'd been doing pretty well. She'd accepted that Spike had a soul, a real one. She'd accepted that she'd come to befriend him, ordering his chip be removed. She'd accepted that Sunnydale had been turned into a crater and that Spike had done it, in theory, for her. She'd accepted all of that and tons more! Tom and Nicole had broken up, for goodness sakes! The world had clearly been lost without her. Going all...wonky.
But this? That Spike would try to convince her that she'd been with him? That was too much. It wasn't even a funny joke. It was just mean. Finally realizing she was just standing there, she jerked her body back from him. "You know that I can verify the crap you tell me," she started. But then she realized he already knew that. That of course she'd run to Willow and Xander and Anya to ask them about this. So unless Spike thought he could trick her within the span of this moment and get her to fall for him, what was his endgame? What purpose did it serve to lie?
"So what is this...you just want to mess with my head? Unnerve me? Play your own twisted mind games? That's sick, you know? Messing with the memories I can't access. I don't know why you'd do this...I mean, damn. I was actually starting to stop hating you so much. You seemed like you'd changed the way you claimed. Like you...like I could talk to you, and count on you - and all of those things that I supposedly did."
She hated to admit this to herself, that she had actually started to enjoy Spike's banter. His stupid text messages kind of cheered her up - to know that at least someone out there was thinking about her. Since all of her friends here seemed to be fairly busy...Spike didn't seem like the worst company.
And now this. He didn't seem to want to discuss it. But Buffy was... - she was furious. He was ruining their possible friendship because of - "This is your stupid obsession or crush or whatever - and I can't believe you won't let it just go."
She felt betrayed, and it showed in her eyes, making her look like some sort of wounded puppy. She was honest-to-goodness surprised and hurt by this turn of events.
"This is what I get for going against my instincts," Buffy told herself aloud, bitterly. "You let someone think you're metaphorically on their side and in bed with them, and they take it as a literal invitation to get in bed with them." A pause. Her voice was shrill now. "And you never even had a bed!"
"How dare you claim to love me. You don't know me. And you don't seem to even be able to care about anyone for more than five minutes. Or maybe...that's wrong. Because you don't seem to have a problem being decent and caring about others like Dawn or Faith - but me? No, I'm special. I'm the one you mess with like it couldn't possibly affect me. Like it really is a game."
She threw her hands up, walking backwards as she kept her eyes trained on Spike. "I don't want to play."