Tā píngshí suíbiàn guàn le, yí yùdào zhèngshì chǎnghé jiù bù zhī zěnme zhèngjīnwēizuò.
He's used to being casual, so in formal settings he doesn't quite know how to sit up stiff and proper.
Tips
history
From the Shi Ji biography of diviners (《史记·日者列传》): Song Zhong and Jia Yi, startled by a profound insight, 'straightened their robes and sat up properly' (猎缨正襟危坐). The phrase captures the moment posture shifts from casual to formally respectful.
usage
Often lightly ironic in modern use, hinting at overly stiff formality. Classic image: adjusting one's robes/clothes before sitting bolt upright to show respect or concentration.
