Welll....ok.
He's just really sort of a douche. :) Really. I always say he was a difficult child who grew into a difficult man, and it's the truth. He was by all accounts a lovely little boy until about three, which is coincidentally when I was born. 
My parents were 18/19 when he was born and he was always sort of babied as a small child, we both were.
We fought terribly throughout our entire childhoods. When we were 7 and 10 we moved to another state, far away from our extended family, and my mother became depressed. My brother acted out a lot starting around 12 and he and my mom started to have an extremely fraught relationship that continues to this day. They would fight, he would say cruel things. She would tell him to stop, that the conversation was finished. He would follow her from room to room, ranting and raving and eventually they'd start screaming at each other. Sometimes she'd hit him. :( (Not like the horrific abuse cases you hear on the news of course, but nothing I'd do to my son certainly.)
When he was 14 he started to get into drinking heavily, and pot and other drugs. When we were 16 and 13 our grandmother came to visit us (our extended family was about a thousand miles away) and one night during her stay she didn't wake up. :( My brother was gone that night and when my Dad went to find him and tell him our Grandma had died, my brother was so far gone (mushrooms I think) that he thought it was a dream until a few days later.
My brother started refusing to go to school and getting arrested for the drinking, etc. I used to wake up in the middle of the night with my parents saying "they had to go out" and I'd know they were going to pick B up at the police station again. I'd wake up again to hear them back and my brother screaming and swearing at them. That year, when he was 16, they decided to let him leave home and he moved in with friends. That didn't work out and my father said he couldn't live with us unless he was working or going to school. He didn't want to do either of those things so he used to sneak back in and sleep in his old room. I remember waking up one morning and my father shouting at him to "get a fucking job!" and just lying there thinking, this is not normal.
He began living with a family in our town and working. I saw him sometimes. He didn't come visit us, though sometimes on Christmas or something he'd stop by. I heard that he was sleeping on the park benches sometimes or from wilder kids in my grade that they'd been partying with him. I sent him birthday cards.
I went to college when I was 18. Things started to get better with my mother and she's mostly pulled out of her depression now. My brother came to visit me a few times. He moved to New Mexico when I was...22 I think? And lived there for a few years. He moved into someone's old, restored chicken coop and helped on their ranch. He was 25 or 26 when he got involved in a relationship with a 17 year old girl and that made things a bit uneasy for him, so to speak. He's always doing that, getting together with very young women. Not so young that I think he belongs on a register or anything, but usually 19-24 or so. (He's 32 now.) I think that it's easier or him, they're still young enough to be suckered along by his bullshit and not make where-is-this going sort of "demands" on him.
When I was 24 I got married and he came for the wedding. I hadn't seen him in three years or so. He got drunk at my wedding but my Dad managed to get him in the car and home before he made any huge scenes.
He decided, on a whim, that he would go back to Ohio and live with our grandmother instead of New Mexico. Never mind that the ranchers were depending on him, never mind that he had a horse and truck that he would need them to sell.
He lived with my grandmother for three years and hated it. I told him he could come here. I don't know why. He's my only sibling, I guess, and so much of our family's lives have revolved around B and don't-make-B-mad and let's-all-walk-on-eggshells-around-B.
He moved into my garage. (In the winter he lives in the basement.) He pays us about $100 every month or so. He doesn't pay for electricity or water or soap or shampoo or laundry detergent. He buys a lot of his own food but also eats a lot of ours. If we're doing a big project (like when we repainted the house) he will help a bit, and if I have to get to work before DH gets home he will keep an eye on DS. It's usually for only 15 minutes or so, though, and I am trying to limit that. He winds DS up a lot of the time and, because he was drinking with people our parents' age when he was 13/14 and sees no problem with that, I don't feel he has appropriate ideas about adult/child boundaries. That's an understatement!
Where the balls come in...well, he'll do things like not wash his dishes. Or he'll come in and make food and leave things all over the counter. I don't know why I have a problem saying, "Hey asshole, come get your crap off the counter!"
There is so, so much more but I think this is going to be The Biggest and Longest Thread Hijack in Mumsnet History, so I'll go for now. And if anyone actually managed to read all that, I salute you. It felt so good to just say it.