Fanon likes to portray Jiang Cheng and Lan Wangji as being jealous of each other because they fear wei wuxian will choose one of them over the other. Which is ignoring the fact that at least in novel canon Jiang Cheng did not even fucking know wangxian ever got along let alone that lwj was in love with wwx until at the very end of the story (in cql canon he does go through a wangxian phase early on and gets very confused by their "breakup" during wwx's sunshot era) and that Lan Wangji is mostly filled with loathing towards both himself and Jiang Cheng for 'abandoning' Wei Wuxian and not being able to save him.
It also ignores the much bigger point that both Lan Wangji and Jiang Cheng are actually jealous of Wen Ning. And why wouldn't they be? That is who Wei Wuxian chose in his first life. He left the Jiang, told Lan Wangji to fuck off no he is not coming to gusu with you, and spent his days with his little-brother-shaped corpse bestie on his mountain in yiling. And then when he came back he immediately called him up the second he could string together more than two notes on a flute. Wen Ning is the real competition. (And he's winning)
- Punching down several trees after kissing his crush (derogatory) for the first time because he has no idea how to process emotions normally
- Randomly biting Wei Wuxian in the cave because he has no idea how to process emotions normally
- Getting absolutely shit faced for the first time in his life and destroying a bunch of shit around cloud recesses before branding himself with the mark his crush from 10 years ago also had because he- well you get it.
- Writing an entire love song for his crush, naming it their ship name, and then only ever singing it out loud once to said crush without him knowing (this is an important tool we'll save for later)
- Generally enjoying being a little shit and then pretending he didn't do anything when people confront him about it
Please feel free to add to this because I know there is much, much more!