There were plenty of reasons, but the frustration just makes it nicer. Or at least, his Wei Ying definitely feels that way, since he always attempts to rile Lan Wangji up. He'd be surprised to find if this one wasn't a total gremlin to try and get his Lan Wangji to, in a way, take out his grievances on him in a more productive and enjoyable manner than beating up trees.

"I will not relax until we are safe."