Ah, but “another think coming” is of American derivation,
I'm in the UK. I never saw or heard 'another thing coming' until I started seeing it on the internet. It's always been 'another think coming'. Which makes sense - if you think this, you'll soon think something else. If it's 'another thing', what was the first thing?
Oh, and if you're in the UK it's arse, not ass. And bum, not butt. Ass and butt are American. (Now awaitng UK people saying 'but I've aways said...')