I've been like this for a long time since my high school (i.e. obsessive thinking, secluding myself in the room for months, destroying shit and doing wacky stuff. For example, punched a hole in the wall, built a block of CD castle in the midnight for no reason and I still don't know why I did it..., and built a fortress with fucking books in the kitchen....] and I am getting better by getting out of the house....also, trying to not care about certain things, which is also fucking hell and i shouldn't be talking about it here...I don't do any drugs, or drink, smoke, etc. I am in a different situation than your brother. It seems that he is pretty fucked up.
on one hand, he sounds like he is sick....he probably can't stop thinking about his self-worth, feeling guilty as hell, which drives him to torture you even more.....he doesn't give a shit about you and your child's food or household things because he doesn't give a shit about his own life...he doesn't live for anything or feels attached to anything other than his own shitty life. I don't think he is doing it to terrorize you...little bit of interactions he does get probably gives him that satisfaction...
eating, smoking, and all the "indulging" that he does is probably a sign that his brain is completely turned off to everything else...
I should probably ask...does he get out often? Is he secluded?
because he could be manipulating you and is seriously fucking evil, not sick whatsoever, etc.
But he had a shitty childhood, right? I am not an expert into that field. I really don't want to judge you and your brother based on my own personal experience. This is just my take on what I think is plausible in his mind.
anyhow...I don't really know your entire situation. He will probably kill himself for sure once all that security goes away and he has nothing else to hang onto. that said, this is pretty shitty and solutions are murky. i don't think there is a bulletproof solution. The suggestion so far seems to be that you should get out. One of things you can do is help him find something to look forward to....because he doesn't know any better or feel like there are better things out there. But if not, then he should probably kill himself and I really do mean it. Sorry for that offensive statement but I always have a thought of suicide and I am pretty immune to its moral impact.
a lot of shit that's being said here is fucking selfish but i guess we are all different when it comes to dealing with family members.