It should be an easy answer. Burning off the alcohol with his golden core had only ever been a loophole, and without it, clearly he should not drink at all.

But they are not in Cloud Recesses, and Lan Xichen has already been drunk here. He hadn't ever intended to, of course, but the wide variety of teas that have been slipped to him have both mimicked its effects and made him more likely to indulge.

He is tired of his life being out of his control. Perhaps it is finally a sign of how well he his not doing that he is seizing on this opportunity to make a decision, even an ill advised one - but he does it anyway.

"I will, but I fear you will find that I have little tolerance for it."