我非柠檬为何心酸因为我就是柠檬阿
[wŏ fēi níng méng wéi hé xīn suān yīn wéi wŏ jiù shì níng méng ā]
Translated directly, it means 'If I'm not lemon why do I feel sour because I am indeed lemon.' This phrase conveys feeling sad or envious using the metaphor of being sour like a lemon.