My phone number on FB?

[Vamp]

You can't get arrested for putting your telephone number on Facebook - in general, stupidity isn't an offence in itself. (You might want to consider whether your FB information is sufficient to commit identity theft, for example)

If you are responding to people "writing...stupid things" then it will depend what you are writing.

The problem might come when your number is used by other people to commit offences. You might have difficulty proving that you were not involved.