Well, since "he has another <something> coming", and think, as a verb, is no such thing, I'd say thing is more like some thing...

Got it? wink Thing, I think.

Edit: Well, those links are convincing. Still, I can't picture the word "think" as a noun. I see the expression "another think coming" more as a joke - which would be fitting in the scene D8a used it.

Synthesis:
Use 'thing' if you think it's right.
Use 'think' if it's the right thing for you.

The only known quantity that moves faster than
light is the office grapevine. (from Nan's fabulous Home series)