[JonInMiddleGA]

At the risk of fulfilling Franklinnoble's prophecy, there's enough sign of chemical imbalance at work here that I'd strongly suggest having that angle checked thoroughly. Much like "being paranoid doesn't mean that someone isn't out to get you", just because there may be some who overprescribe medication for kids, there are also situations where it is the key to effective treatment (think schizophrenia as a possible example).

Beyond that, there's another thing that jumped out at me in your post --
If (or more likely when) he decides to disobey he gets something of his taken away ... The problem is, he still just doesn't understand - he looks at you like you're the meanest thing in the world and repeats the behavior again.

That's two unrelated things AFAIC. You may seem like "the meanest thing in the world" but that's the breaks sometimes. That has nothing to do IMO with "...and repeats the behavior again". That seems like an indication that your application of the punishment isn't failing you, it's your choice of punishment.

What I'm trying to say is that if it isn't working, then there's a chance that you're choosing the wrong punishment; i.e. taking the wrong toy, restricting the wrong privelege, etc. You aren't striking at something that really matters, or at least not
at something that matters enough to restrict the undesirable behavior. Different kids react best to different motivations, maybe it's a matter of finding the most effective carrot and/or stick. (FTR -- I'm not saying you haven't tried to find the right one(s), I'm just suggesting that you take a step back & re-examine your choices to see if there's something you might have missed, sometimes it won't be something obvious or even logical.)

Having a son who is in the same age range (not quite 6 1/2), I can at least imagine your frustration with this & I sincerely wish you the best.