柠檬精 (Níngméng jīng) is a new and popular internet slang in China, and typically is used to describe a person who enjoys criticizing others who appear to be more successful, and happier than oneself.

In China, “柠檬 (níngméng) lemon” and “醋 (cù) vinegar” have one same trait —— “酸 (suān) sour”.

“醋 (cù) vinegar” is often attributed to jealousy. Interestingly, they are both used in the same context to describe a jealous person, such as “吃醋 (chīcù)”.