He might not get it. He might think it's self-deprecating humor--he might, honestly, think that he's being funny and humble and relatable. Seriously.

It's worth asking him in a gentle confrontation.

He might also just not know how to get POSITIVE attention.

I know something that rocked my mindset (though I'm not sure how to make it practicable here): we did an exercise in a workshop I was in where we wrote down all our negative self talk. Then the trainer asked us "would you talk like that to your closest and best friend? Would you tell them 'you suck, you're so terrible, you never do anything right'?"

Yeah, well, if you wouldn't talk to your best friend like that, why are you talking to yourself like that?

Another nugget: Cheri Huber, my favorite American Buddhist, said (and I'm paraphrasing) that if beating ourselves up actualy worked to make us improve, we'd all be perfect by now. Beating yourself up doesn't work as self improvement.