The camera follows a random cute gay dude over to some intense cinematography where like, Dan is foregrounded with fuzzy S in the back, and then vice versa, and then they look at each other, and he makes this funny heard-jerk toward the dance floor and that godawful song is still playing, and they go "dance" some more, which is outrageously awesome. Dan immediately goes, "So you're going to sleep with Aaron for the first time tonight, I heard," and Serena's like "I will smack that girl Lexi into tiny tiny pieces" and Dan's like, "No, I just thought that friends talk about these things." Which they ... don't, usually, and not fake ex-boyfriend "friends" ever, and Serena goes, "Well, what's there to talk about? We've been dating for a while, we've gotten to know each other. It's not like we're rushing into anything." She can't meet his eyes, because this is undeniably creepy to be doing, period, so she goes on the offensive about how the relationship is important to "some people," for example "people who are not Lexi," who is a "whore," and Dan pretty much prematurely ejaculates all over his rented Brooklyn tuxedo.
Which is... Not what Serena was expecting, I guess, although maybe she just doesn't know heterosexual high school boys very well, having never met one, and thus doesn't know that Sex > Everything Ever, so she's disappointed that he views the sex with Exie Lexi with a certain amount of anticipation. He's like, "Except for that hummer I got from Georgina Sparks I really didn't think sex was in the cards for me right away, so that's great news." Offended, Serena goes slightly overboard about how she always thought sex was a bit more meaningful to him than that, and his response is beautiful, and so right on, and so completely inappropriate all at once: "Well, it is. Especially when I haven't had it in a long time." See, this is the Dan Humphrey I understand. To his credit, he immediately realizes he fucked that one up, but it's too late: Serena plasters that Rhodes women smile on her face and vanishes into the crowd. Before he can follow her -- what is with Humphreys losing people in crowds? -- Lexi appears and commandeers him away from the scene of the awesome crime.