How do you say that is not funny in french?

There are a few ways to say "that is not funny" in French, depending on the context and desired level of formality:

Formal:

* Ce n'est pas drôle. (This is the most literal and neutral translation.)

* Ce n'est pas amusant. (This emphasizes the lack of amusement.)

Informal:

* C'est pas drôle. (This is a more casual and colloquial way to say it.)

* C'est pas marrant. (This is another informal option, meaning "it's not funny" or "it's not cool".)

Adding emphasis:

* Ce n'est vraiment pas drôle. (This emphasizes that it is definitely not funny.)

* C'est pas drôle du tout. (This means "it's not funny at all".)

Responding to a joke:

* Je n'ai pas compris. (I didn't understand.)

* Je ne vois pas l'humour. (I don't see the humor.)

* Je trouve ça un peu lourd. (I find it a bit heavy/unfunny.)

The best way to say it will depend on the situation and your relationship with the person you're speaking to.