quote:I think if not being treated in its full version is if he's not being treated, which can mean "now."
Yes, that is one way. But 'gets' also works.
And, if we use the original sentence with 'treated' -- If not treated with the respect he feels due to him, Jack is going to get / will get very ill-tempered and grumble all the time -- is also correct.
So, I do believe that both 'being treated' and 'treated' are OK for the given sentence.