The Chinese phrase 吃醋 (chīcù) literally means "to eat vinegar". "吃" means "to eat", while "醋" refers to vinegar, a kind of sour seasoning. However, the word "吃醋" also has a figurative meaning of "feeling jealous". This phrase is usually used between a couple.
“吃醋（chī cù）”的英文字面意思为“to eat vinegar”。“吃( chī)”相当于英文中的“to eat”。“醋”则是指一种酸味的调味品。“吃醋”比喻产生嫉妒情绪，多指男女关系方面。
There is a story about this idiom.
Supposedly, the story happened in the royal court of Tang Dynasty. It goes like this:
Emperor Taizong (唐太宗, táng tài zōng) decided to choose a concubine for his premier Fang Xuanling, in order to win Fang's loyalty. But Fang's wife, being extremely jealous, opposed bitterly to the emperor's decision and would not compromise at all. The emperor had to challenge her by ordering that she should end up with either drinking a cup of "poisonous wine" or accepting the arrangement. Unexpectedly, Mrs. Fang was such a strong-willed woman that she tossed off the wine without any hesitation. The "poisonous wine", however, turned out to be thick vinegar tasting sweet and sour. Since then, "吃醋" has been figuratively referred to as jealousy.
For a couple, if either party is attracted by or flirting with someone else, the other party can say "我吃醋了"(Wŏ chī cù le, I am jealous of your relationship with him/her).
dāng tā fā xiàn tā tā ài shàng bié rén de shí hòu ，tā chī cù le
He felt jealous when he found that she fell in love with someone else.