We have a very cool phraseologism in Polish: napisać/zapisać kredą w kominie. The literal translation is: to write with a chalk in a chimney. And the meaning is to emphasise that something rare and extraordinary has happened. For example:
"She has agreed with me. I'll write with a chalk in a chimney."
So, please write with a chalk in a chimney, that I have cleaned the bathroom.
Please note, this sentence also contains a bit of autoirony, but that's another story.