寂寞的人请吃苦瓜
[jì mò de rén qĭng chī kŭ guā]
Translating to 'Lonely people eat bitter melon'. Bitter melon has a notoriously bitter taste, hence it's used metaphorically to mean lonely people endure bitterness and suffering. It could be an advice that being lonely comes with difficulties or hardships akin to eating a very bitter fruit.