Book search - 'cancel' out bad thoughts

[Demeter]

Hi, a few years ago I read a book (non-fiction) (depending on your point of view of course) that advised to say the word 'cancel' if you said something in jest that you then regretted as there is no humour in Universal Law. Saying 'cancel' would effectively cancel out the strength of the words - does this jog anyone's memory and can you tell me the title/author? Oh, that sounds so vague, doesn't it?! Thank you all in advance...