我是柠檬为谁心酸
[wŏ shì níng méng wéi shéi xīn suān]
Loosely translates to 'I'm a lemon who has a heartache for whom?'. 'Lemon' here doesn't refer directly to the fruit, but instead is colloquially used to imply sourness or jealousy. So the expression carries a connotation of suffering from heartache, envy, or bitterness.