Vanessa complains that additionally her hands are tied because she can't "confront" Catherine, because the Butler would remember her visit. Vanessa is using the word "confront" in this instance to mean "blackmail," which is a felony. "...And she'll drop the dime on the Captain," Dan follows up, causing Vanessa to give him the sour look you would give anybody who said something that queer at a time like this. She's like, "And yet I can't figure out how to fuck everything up using these photos of a person fucking her own child. Just can't put together how this might be of use. Tell me what to do." Dan's like, "Wow, me neither." They stare blankly into space. "Well... You're not gonna like it. Blair." OBVIOUSLY. I'm proud of Dan for figuring it out this quickly, but my God, when are they going to learn that you're supposed to play it like this: "I have a problem, what should I..." -- Blair. Always. It's that easy, people. You always ask the busiest person you know -- not the person who talks about how busy they are all the time, but the actual busiest -- because they always have the most time and resources to help. Duh.
Vanessa cannot trust Blair. Dan's like, "Nobody on this planet can except for Serena, but: if you Google revenge, you get blairwaldorf.com." That's a funny line, admittedly. He reminds V of how Blair helped with the Georgina Sparks situation when he was finally smart/brave enough to call her, and she will [always] know what to do. Plus, "When she sees this photo, she will be plenty motivated to do it." Vanessa's like, "Oh that's right, this is her future husband. So I can show her this and get Nate saved, but..." Yes. Blair will most likely slit your throat. True. But hey, you're the one with the drama queen love affair happening in your head where you're sacrificing "everything" (i.e., nothing) to help Nate in some fashion that really only makes sense in your lovely, empty head. Vanessa puts down the phone and stares at it like it's nuclear while Dan ditches her to go bitch at Serena for her hideous and venal crime of ... letting the new girl in school eat lunch with the most popular girls in school on the first day of school.
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.