Lan Wangji knows lots of important information about his friend, like that this is usually the time when he decides to go wandering around the library looking for mals, and therefore Lan Wangji can seamlessly join him and hit the mals that look more amenable to swords than spells with Bichen. 

He does not, however, know his name.

After some reflection, Lan Wangji has concluded that this is probably a violation of the rules of friendship. 

He has written out the appropriate sentences in IPA and put them in his pocket. He removes the piece of paper and reads, "What's your name?"