I love this way English has of swallowing and digesting terms from other languages. https://www.oed.com/dictionary/the-tooter-the-sweeter_phr

Quelle surprise (wink wink)!

This is the first time I've ever seen "toot sweet" used. The more you learn :)

To be clear, it’s a jokey informal English language term, not a standard one.

“The English language doesn't exist, it's just badly pronounced French” strikes again.

There's also the UK practice of deliberately mangling French for comedic effect, as in Del Boy's cries of "Bain Marie!" and "chateuneuf-de-paper!" on 1980s TV. Saying "Toot sweet" can fit right into that bucket.