My brother is 2 years older than me (I am 32.) He is a well-meaning person. By that, his heart is definitely in the right place, however, his lack of regard for societal 'norms' is a massive worry.
We were both brought up in a fairly standard middle-class household and were definitely taught good manners, yet my brother has none. I don't mean using the wrong knife at the dinner table or similar but really basic stuff. I know my mum and my dad set a good example to us in how to speak to people and were strict (not overly so but had high standards) with please,thank you, and excuse me.
This is my brothers actual way of going about things - we went for lunch today in Pizza Express: not highbrow but nice enough. He wore mucky, torn jogging bottoms and a huge hoodie - two sizes (at least) too big. This is his staple outfit, getting dressed up involves a pair of jeans.
He pesters the waiters - 'when is it coming?' No please or thank you. He shovels food in and chews with his mouth open. If he has a hot drink, he slurps it. Loudly. If he coughs or sneezes or burps, he does so loudly and unashamedly. Not even as in 'that's funny' - just does it, like no one is around him. He slouches in chairs and yawns loudly - very loudly - and doesn't cover his mouth. His teeth are not good - the back ones need a lot of attention, and yawning like this is really unpleasant. Farts unselfconsciously.
Then there's the lack of regard for other people - he constantly says 'well so? Nobody knows me!' He urinates not quite in public but will turn his back and pee - fair enough in an emergency but in a public footpath? With public toilets minutes away? In town today I said, 'I'll get some cash out' He BELLOWED my name, so people stopped and stared, rather than come and get me.
I am constantly apologising for him.
The heartbreaking thing is, he is desperate for a girlfriend and is very, very lonely. He has a small handful of friends from school days but their wives and girlfriends, now, dislike my brother and refuse to spend time with him. 
I want to help. Yet he won't let me. He just says 'no one knows me/I wouldn't do (fart/yawn/sneeze) out with a girl/ I wouldn't wear a hoodie on a date.' He can't seem to see its part of a general impression he gives - of, I hate to say it, a complete tramp. His house is disgusting as well.
When I pictured us being adults together I wanted a friendship. As it is, I find it REALLY hard to spend any length of time with him as his habits are crude and frankly,nauseating.