When autocorrect meets "buttock-clenching", I'd guess.

You are correct sir or madam! I’m leaving it though, I like the sound of it.

Oh. I figure out what it meant, but I thought it was meant to be a ‘polite’ version. Sort of like saying ‘shucks’ or ‘darn’.

Autocorrect didn’t enter my mind as a possibility.

That's how I read it. I had to go back and re-read it to see it says "butter" actually. I guess I've successfully installed anti-autocorrect in my brain.

butt clenching

https://www.dictionary.com/browse/buttock-clenching