柠檬高攀不起西瓜的甜
[níng méng gāo pān bù qĭ xī guā de tián]
This username conveys a feeling of inadequacy or inferiority when comparing oneself to someone or something that is much sweeter or better. Lemons are tart while watermelons are sweet, implying that 'I' cannot compare with someone's good qualities or successes.