No-no

Division by zero is a big no-no in mathematics.

Source: tatoeba (2928693)

That's a no-no.

Source: tatoeba (8914559)

Smoking is a no-no in hospitals.

Source: tatoeba (9920318)

Japanese like the number 14, which they interpret as meaning "to die alone"; however, the number 24 is not really popular amongst Japanese people. Such numbers are a no-no to Chinese, who think that the number 4 is just unlucky; however, that number is sacred to Japanese. The number 54 is acceptable to speakers of Cantonese, for whom it means "not dead." Chinese prefer the number 3, the "life" or "birth" number. Japanese and Chinese people have different cultures, of course.

Source: tatoeba (10538968)