Back at Gillian's brothel, it's time for her to scold Richard for talking out of turn to Tommy earlier. She prefaces her remarks by asking Richard if he likes living there, so she's not above holding that over his head. There's a part of her that's kind to him, so long as he's amenable to her whims as far as Tommy is concerned (and he is, at least at this moment), but it only goes so deep. She asks him if he's going out tonight, and he says he is, to meet a friend. Now that should've been your first clue.
Back at the party, Nucky has cleared out the servants' quarters so he can hold a business meeting with Rothstein, Remis, Luciano, Lansky and Rosetti, the latter of whom is behaving like a real asshole with everyone else. He starts right in on Nucky about the 500 cases of rum he wants, but Nucky stops him short. There's going to be a new business policy in the new year. As a favor to his political cronies, he's going to streamline his business so that he's selling all his liquor to only one buyer: Arnold Rothstein. If they want it, they can buy from him. Rosetti correctly infers that it'll be at a ridiculous markup, and he can't exactly get his liquor from elsewhere -- Brooklyn's main bootleggers won't sell to Italians, for instance. Rosetti then resorts to childish name-calling, starting with Nucky but really just going around the room like he's Don Rickles all of a sudden, calling Rothstein a "smug kike prick" and threatening to fuck up Luciano and Slater. He calls Nucky a "breadstick in a bowtie" (stealing that) and a "pasty cocksucker." Nucky warns him to slow his roll, and offers to comp him at the Ritz in order to have him chill the fuck out. Rosetti just demands his 500 cases of rum, but he's not getting them. With the whole room against him, Rosetti makes a weak "Nobody here can take a joke" claim, then storms out with that poor Uggie dog under his arm.
Upstairs, Rosetti is still fuming, as the guests count down to a happy new year. He charges across the room towards Margaret, and you start to worry that he's going to do something awful to her. Instead, he just hands her the Uggie dog, all "Take it! And make him an over-precious star of an emptily nostalgic Best Picture winner!" And even though he doesn't harm her, I'm still awfully unsettled that he had his eye on her like that. Nucky seems to be thinking the same thing.