Meaning:
“天” means “sky,” and “菜” means “dish.” While in English people say “someone or something is my cup of tea” to show one’s affection for the subject, in Chinese, people would say “someone is my ‘dish.’” This term, first used by gay people in Taiwan Province, became known to netizens throughout China, and is now used to refer to those who are very cute or strongly appeal to the speaker because of their nice character. Fans also use it to address their idols.
Example:
A: 过年你去哪儿了？
Guònián nǐ qù nǎr le？
Did you go anywhere during the Chinese New Year holiday?
B: 就在深圳。其间参加了一次同学聚会，遇到一个天菜女生，奇怪怎么上学的时候不认识。
Jiù zài shēnzhèn。Qíjiān cānjiā le yīcì tóngxué jùhuì，yùdào yīgè tiāncài nǚshēng，qíguài zěnme shàngxué de shíhòu bú rènshí。
I stayed in Shenzhen. At an old schoolmates’ gathering, I met a very cute woman. I was wondering why I never met her on campus.