You're not rewarding bad behavior, you're seeing his bad behavior as a communication of a need, and meeting that need. Punishing the behavior, or refusing to meet the need to teach him a lesson, would accomplish nothing; it would not teach him skills for dealing with unmet needs, it wouldn't teach him to use other communication tools to let you know, it wouldn't teach him to prevent his need from going unmet... it is pointless.
I have two thoughts - one is to talk to your son about why you're going out. "Wow, you're getting really grumpy. You seem to be feeling a little out of control! You must be needing some fun time out of the house," or whatever is going on in the situation. This starts him on the path of doing this for himself when he's older: recognizing his emotions and behaviors, and looking for the need behind them. Also, you might be able to predict when he's going to have a melt-down, and head it off at the pass. If you can look at the situation and say to yourself, "Ugh, Ds is probably going to be wailing later..." then you are seeing that he's got that need. Try meeting it then, tight away, preemptively. This way there's no hint of rewarding him for bad behavior, because you're meeting the need before it's built to the point that he explodes. You eliminate two conflicts at once (Ds' meltdown and Dh's criticism) if you are able to do that.
And I love the "get your beans out" phrase from a PP! Fun and meaningful for a child, and nonjudgemental from the parent.