Serena finds him immediately once he's back on campus, and immediately starts apologizing for letting things get as far as SUSHI, and Dan rocks back on his heels, more smug and vindicated than maybe ever: "And that answers my question." Um, what question would that be, chumbucket? "I wonder if Serena is kind enough to realize that two wrongs don't make a right, and no matter how shitty I was for hitting on other girls in front of her, she isn't going to hold it against the girl?" Because what she's doing, Dan, is answering that question. You are correct.
"Look, Blair invited her to lunch, not me." Dan points out that she was there, and Serena's like, "Yeah, until I told Blair to knock it off and left to come find you just now." And oh, the condescension: "So you were part of it, and then you had second thoughts?" YES. I realized I was doing a shitty, junior-high thing, and cut it out, and tried to make amends. I wonder if anybody else here is also doing shitty junior-high crap they could be knocking off right about fucking now? ...Nope. "Really? Because it sounds like you're just trying to rationalize." She sighs and makes the sad face at him, but he's too gross to be overpowered that easily anymore. "Look, it's just ... We knew that this would be awkward. You know? And I just assumed that it would be more of a sad awkward, not this ... competitive awkward." Which it was, until your ass got competitive.
"I didn't think you'd enlist backup," he says, which is ... a fair point, really. I mean, it's not S enlisting the backup, but she does have this rabid pitbull that nobody can knock loose who automatically applies. But the yucky thing, which is to say the thing that Serena balks at, is not the Blair part, but the part where Serena needs "backup." That's just rude. The idea that Dan was just blamelessly walking through life while horrible girls threw themselves at his feet (or he knocked them there, with his stupid ass), as usual, and Serena like can't handle it, and went running to her bitch friends to alienate the girl and keep the two of them apart. Blair yes. Serena? Never. She throws parties, Blair throws knives. She's the Queen by existing, Blair's the Queen by rocking it hardcore. (And by the end of this episode, B's going to need to change her name to Trouble if she's going to stay alive at all, so look for movement on that front as well.) There's nothing shameful in the way that Blair accumulates and retains power -- it is way awesome in fact -- but it's just not how Serena rolls, and if she ever did it that way she'd look ridiculous, and feel ridiculous. Her power comes from magnetic awesomeness, not from scheming and fixing and destroying and planning. That's too much like asking.