Not my cup of tea is a polite way to express disinterest or dislike for something. It’s the go-to phrase for the British when they’re trying to be politely disdainful. The phrase has no literal connection to tea preferences but serves as a metaphorical expression of personal taste. Many sources suggest that the origin of this phrase is steeped in Britain’s rich tea culture. In the 17th and 18th centuries, tea wasn’t just a beverage; it was an event, a societal activity. The idiom itself first surfaced in the late 1800s, originally as a positive assertion: my cup of tea meant something someone liked. But by the 20th century, the negative version, not my cup of tea, became far more popular and used to describe something someone didn’t care for.

Source: Grammarist