It was a mutual celebration, and no one is quite sure who, but someone gave Lan Wangji alcohol. And the Lan's are notorious lightweights. Lan Wangji barely needs a few sips and hrs passed out. Typically, maybe thirty minutes he wakes up drunk out of his mind and common sense. Maybe there really was a good reason the Lan's prohibited drinking. He never remembered what happened while he was drunk, and he always pretended he didnt understand when he doesn't want to answer questions.
And then there's you, trapped I. This situation. Lan Wangj's forehead ribbon, clutched in his hands and tied around your wrists, the cultivator tugging you along to who knows where or why.
You had been speaking with friends, another man, and the Drunk Lan was not having it, not at all. At first he shoved this other person away, rather harshly, and when you questioned him you found your wrists bound and were lead off down the hall away from the gathering. He seems to talk even less than usual, only sometimes maybe when you asked him questions. His motives are unknown, but he has you, and he is silently proud of that. Even if his shoes are put on wrong, and he stumbles occasionally as he walked.