4. Serena: Two days into the trip, Poppy and Gabriel get in this huge fight, and then she just leaves, abandoning me and Gabriel. And so I stayed around to keep him company.
Dan: Well, you did a bang-up job.

bang-up: excellent, very good

5. Rufus: That's Allan Levy, the art collector. He's the guy who put a Monet in his bathroom. I…Oh, no.
Lily: Well, he's an old friend of Cyrus. You've been saying the mid-range art market is dead, so I thought it might be nice for you to meet a few high-end collectors.
Rufus: No, Lil, I appreciate you trying to help, but I am not fawning over an ass like Allan Levy just to make a sale.

mid-range: 中端，高端就是high-end
fawn over someone: to flatter someone or attend to someone excessively; 拍某人马屁，讨好某人，也可以说 to curry favor with someone或者更粗鲁一点的就是to kiss someone’s ass

6. Serena: I'm sorry that I snuck out, Mom, but I had to see Blair. She invited me to Seder, so I invited Dan.
Dan: Though Blair is now strangely nowhere to be seen.
Lily: Well, lucky for you, I don't want to cause a scene at Eleanor's. We'll talk about this later.

sneak out: 偷偷溜出来，snuck是sneak的过去式
Blair is now strangely nowhere to be seen: B都不知道跑哪里去了
cause a scene: 在大庭广众下训你，to be loud and rude with other people or in public