Lan Wangji is so funny in donghua episode 2.
"that man's a lunatic that will go after men, women, trees, flowers and animals! wei wuxian would never take his body!"
Lan Wangji hears this, see's Wei WuXian's brief wtf? face about it and holds his hand up to his mouth to hide one elegant huff of laughter. Then he's silent as Wei WuXian taunts and mocks and riles up Jiang Wanyin. Then Wei WuXian says outright he's his type and Lan Wangji can't stop himself from a self-satisfied stroke of his guqin. Then he gets to start dragging a loudly protesting but not at all resisting Wei WuXian to the Cloud Recesses.
In the entire interaction, this is the only moment he closes his eyes, shutting out everything around himself to collect his composure.
Wei WuXian, who flirted with him relentlessly (though they didn't really know that then) and flirted casually with all kinds of people in front of him, having to deal with the negative consequences of flirting with the "wrong" people for a change.
You cannot tell me that isn't a look of brief, hilarity-filled schadenfreude.
Lan Wangji went from having a slightly unusual nighthunt to having the time of his life at everyone's expense.
More seriously for this scene: the framing/context of how Wei WuXian backs into him while playing his terrible-flute version of WangXian is so clever.
We don't see him come up behind Wei WuXian after getting close enough to see him, see him controlling Wen Ning and confirm he's the one playing WangXian. We don't see him freezing in shock and wonderment. We don't see any fought back tears or wrestling with a mix of joy and anguish in any way. We don't hear any cry or word or sound he might have made.
We just see Wei WuXian's torso back into him, then see his hand move to grab Wei WuXian's wrist like it's a reflex and hear him take in a shaking breath as if he'd been holding it, or it had been punched out of him and he's taking in air after being "revived" from the shocked state he'd fallen into by contact with Wei WuXian, solid and real and pressed up against him.
Also interesting is the frown he gives to Wei WuXian's arm as Wei WuXian is thinking he has to get Wen Ning out of there. Wei WuXian's arm sways back and form and Lan Wangji's brow furrows, but then Wei WuXian starts playing. As soon as Wen Ning is gone he drops the flute, then slumps, and Lan Wangji immediately lets him go.
I think what happened there was Wei WuXian tested Lan Wangji's grip, felt it was solid and played with his wrist caught; Lan Wangji felt him testing the grip and wondered if he should let go, but then Wei WuXian remained unresisting, so since he didn't want to let go he kept holding on while he played. Then, when Wei WuXian went limp in a way that would have broken his grip, Lan Wangji let go.
This jives really well with how, right after, Lan Wangji doesn't stop Wei WuXian from running away, or from coming back.
He battles off Jiang Cheng's attack when he's right in the line of fire, lets Wei WuXian step into the attack when that's what he wants, then becomes an immovable wall when Wei WuXian makes it known he wants Lan Wangji's protection.
And this is shown visually. Lan Wangji is a step back when Wei WuXian is talking with Jiang Cheng about who he really is, watching and listening attentively - getting the scope of the situation and figuring out what Wei WuXian is doing/wanting at that moment so he can respond.
It isn't until Wei WuXian throws himself behind him that Lan Wangji really locks in, but more importantly that's when he speaks for the first time.