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

7.
Eleanor: Serena, what are you doing here?
Lily: Blair invited her.
Eleanor: Strange. Blair made it absolutely clear that she wasn't going to be here, but please stay. Daniel, would you go downstairs and get the kosher wine and could you please make yourself a little more presentable?

made it absolutely clear: 说的非常清楚，表达的很明确。如果你问别人“听清楚了吗？我说的够明白了吗？”，英文就是Am I clear?
make yourself a little more presentable: 穿的整齐一点，看上去拿的出手一点

8.
Nate: Most of you know me. I'm Nate Archibald, Tripp's cousin. When Tripp asked me to be the best man in his wedding, I was a little bit surprised, to say the least.

to say the least: 毫不夸张的说，at the very least; without overemphasizing the subject; to put it mildly

9.
Gabriel: Why won't you even talk to me? I mean, after everything that we've…
Serena: Because Dan is my boyfriend. We got in a fight before I left for Spain, and once I got there, I got a little carried away, but no matter what, I had to come back.

carried away: 兴奋，忘乎所以。to move or excite greatly. e.g. We was carried away by desire.

10.
Blair: Cyrus, I apologize about missing the Seder and being so snotty about N.Y.U.

snooty: 傲慢无理的，impertinent; arrogant.