「你唔係我杯茶」

這句說話是直接翻譯自英語中的一句成語 "not my cup of tea"。

因為西方人說話比較喜歡使用比喻，而且西方人交談的禮儀中比較顧及對方的感受，直接拒絕說「不喜歡」或許會傷及對方的感受。所以當在需要客氣的場合，不方便直接拒絕人家說 "I don't like it" 時，便會婉轉地說 "this is not my cup of tea"，好讓對方知道「那樣東西並不適合我」或「那並非我想要的東西」，並非一定是對方的錯，或是那樣東西不好，只是我覺得不合適而已。

You are right, it was translated from English and I think it just happened rather recently (probably about ten years or so) when compared to other long-time (hundred or thousand of years) Chinese idioms or sayings.

Like the Chinese, western people also built up new words and expressions from its day-to-day activities, culture, etc. English people like socializing with friends and drinking tea; and my cup of tea was extended to mean my favourite (as you won't do it everyday if you don't like it). Thus, when people say that a person or a thing is not my cup of tea, then it means that the eprson or the thing is not his type, implying he does not like it.