嘴角上扬看尽世态炎凉
[zuĭ jiăo shàng yáng kàn jĭn shì tài yán liáng]
The literal translation is 'smiling wryly at the world's vicissitudes'. A bitter-sweet smile showing acceptance and nonchalance while observing changes in life and relationships, indicating maturity, wisdom and perhaps sadness.