While I think that Arial is off base here about how creatures can be defined, he's still just arguing that you should be consistent. He acknowledges that you are free to rule that chickens are not creatures, and therefore free to rule that you can't hex a chicken. So again: not a claim that you are a bad DM if you don't allow the chicken hex.
At least that's how I'd read it. Maybe he will chime in and correct me, and he does think that a DM disallowing the chicken hex is bad. If so, I think he is wrong.
But that doesn't make your claim right, that a person suggesting the idea is a bad player.
It is interesting that you are amazingly charitable to those you fundamentally agree with, and yet cannot seem to see the innumerable posts that others seem to take issue with.
I mean, either all the other people here are absolutely crazy and just misinterpreted the many, many posts in this thread, or perhaps there is a tone that you don't wish to see.
Either/or. I would refrain from making comments similar to "no one in this thread has said or implied X" when, at the very least, it takes a whole lot of 'splaining to avoid the obvious quotes.
Anyway, I think you miss the point re: the terrible player. It's not that he demanding "Good Faith" or "Consistency" from the DM.
Instead, he is trying to leverage areas in the rules to his own benefit, and looking at the rules not in a holistic fashion, or for the good of other players or the game, but instead attempting to contort them to his own benefit.
Look at the example you just use to support that poster. Now, if you want, you can go through and make a specific ruling as to what each and every example of "creature" in the PHB exactly means (there are 1,908 of them). After that, you can do "it".
Because there aren't defined keywords, like "Attack Action." What you keep overlooking is a player that is using sophistry to demand a foolish consistency is just being a jerk. A DM who is consistent in their ruling (a chicken or rat does not activate hex, for example) is consistent. That's called A RULING. And a consistent one at that.