心有柠檬
[xīn yŏu níng méng]
Means 'heart filled with lemon'. Using 'lemon', commonly associated with sourness, could signify having a slightly bitter taste in one's life but also potentially the freshness and vitality brought into it. Alternatively, could playfully convey a mix of sweet-sour emotion in romantic contexts similar to the bittersweet sensation given by lemons.