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...
Actually, while rarely used as one, "think" is, indeed, a noun.
This is a really interesting website on the "thing" vs. "think" debate, as well, and pretty much covers everything you ever wanted to know about it
.
Oh, and please don't get me started on "I could care less." Yes, I'm a stickler for this kind of stuff. If you think I
couldn't care less, you've got another
think coming
.
