"She'll be bound by their laws," Chuck explains very dramatically. "Namely, she won't be allowed to date ex-boyfriends; namely: you." Dan is grossed out and swears Serena wouldn't do that. Because you know what's tacky? Not standing by while your boyfriend starts dating some random ugly girl on the first day back just to hurt you. And Serena is not tacky! Chuck smiles and smarms away, begging Dan to prove him wrong. Dan stands there and thinks, and before you know it he's whipped himself into a frenzy once again of how much he fucking hates his girlfriend. The phone rings, and he tries to blow V off, but eventually she tells him she's having an emergency of the creepy eavesdropping variety.
Sushi for lunch on the Constance steps, as the Met is under construction. Serena says "this" is wrong, and B pretends not to know what she means. Serena corrects her fake misapprehension, nodding toward Amanda. "Amanda?" S nods, and B speaks up: "Amanda. We have a few ground rules here." Amanda's funny: "...For lunch?" B gives her a fake laugh and cuts through the BS: "Now that we're all friends, you should know that dating someone's ex is frowned upon. For instance, Serena and Dan used to..." Serena is bugged by all of this, but doesn't say anything. Amanda says she didn't know, and Iz and Penelope rush in to comfort her. "Of course you didn't! That's what friends are for! But now that you know... " Amanda reluctantly says she's "pretty sure" she gets the picture, and Blair pulls out a gun: "Pretty sure?"
In order to save a life, Serena sends Amanda to fetch her some gelato. That's hilarious, that Serena's protecting this girl by ordering her around. "My treat!" Amanda leaves, grateful, and S tells Blair this is not how it's going down. Blair is literally confused, like her brain won't cogitate the problem here. S runs off to apologize to Dan immediately for even letting things get so far as SUSHI, and B's like, "But it's still for your own good!" The unspoken "I'm going to do it anyway!" is not really S's problem. Except it totally is. B crosses her ankles and worries about the hit she ordered on Amanda this morning, and if S is going to bitch about that too.
Dan and Vanessa stare at the pictures of Catherine and Marcus and try to hide their boners and say all kinds of "Why can't I look away?" type of crap, and Dan's like, "Bottom line this for me. Telling Nate?" Oh God no, that would involve losing the precious imaginary thing she has over him that makes her his tragic one true love, so why on earth would she do that? Or, as V explains, "He would most likely freak out." Dan agrees. Have any of you motherfuckers ever met Nate? He wouldn't freak out in any way, because he would barely understand it and can barely manage to care about actual shit. He would laugh, and then go give Chuck his 4:30 blowjob just like any other day, and if you mentioned Catherine or Marcus to him an hour later he would be like, "Who? Nope, doesn't ring a bell. Wanna go shoot some hoops?"