Nate gets tired of the total constant pushing that is the Blair Experience, and barks at her a little bit. She asks him what they could possibly have to discuss, beyond boning and getting married and naming their kids Paul and Holly, and Vanessa -- who is standing there, on legs that are fully operable, staring at them while they have this conversation -- literally asks them to go away and talk about it somewhere else alone. Which on the one hand, Blair should really pull this shit in private, but also: that is so Vanessa. Blair points out that she's standing there gapemouthed, and pulls Nate up and away.
Up in Chuck's room -- Because where else would she pull this shit? If you really think about how gross you were in high school, doing things just for effect and using people to make points to other people, you would go insane -- Nate's like, "What up." Blair throws him across the room, onto Chuck's bed, and tells him they're not leaving until they figure out their status. She scrambles on top of him, and he looks up at her like he has a concussion or chronic ennui and can't quite fight her off, and she's like, "Do something!" He's probably just used to getting the cash up front.
Nate squirms underneath her and says something very awesome and unbeatable: "Blair, stop acting like me being your friend is some kind of plot to humiliate you, okay?" Ouch, that is such a good line. Way to turn it around on her, kid. "Did you ever think that maybe things didn't work out between us because we weren't friends?" But Blair Waldorf will not be denied! She plasters on a creepy fake smile and wiggles all over him about how he's so right, and they've become such great friends in the last week, and it's just this magnetic force of friendship that is making her have to kiss him. Nate laughs as she goes in for a third time, because she's so crazy and funny, and tells her to tone it down.
Blair pushes it just a little too far, caught up in the moment and remembering the filthy things they used to say. She suggests the party crowd -- or even grosser, Chuck and Vanessa possibly eavesdropping -- could be a turn-on, rather than a totally sad sign that desperation is alive and well in here. Which is not only a bad idea to say, but so the wrong way to go with Nate, man. He says her name, very firmly, to snap her out of it; she gets embarrassed for getting weird with Nate, so that when he touches her hair to comfort her, she jumps away and yells, bizarrely, "Only my boyfriend gets to touch my hair!" I don't know what that's about, but it's certainly a buzzkill.