To use one of my favourite malaphors: he has had a, “I'll burn that bridge when I get to it” mentality.
Or as noted already, he’s the perfect demonstration of the adage: be careful how you treat people on the way up, because you meet the same people on the way back down.
He has a strict method for dealing with criticism that he never appears to deviate from. In any given situation his instinctive response is to claim that any criticism is grossly unfair for handful of recycled reasons: it’s not so bad, others did worse, why are you picking on me, you’re a bully, my mental health, see what I have to put up with. Rinse and repeat. It’s difficult to fathom, because it’s not how most people operate, but it genuinely doesn’t appear to have ever occurred to him to actually ask himself whether criticism of him is valid, about anything, ever, in his whole life.