Some people where baggy trousers to hide their body size while others they think it's cool. A theory states that hip-hop icons co-opted the look from prisoners who were given one size fits all pants but no belts.
If you are referring to the people that wear their pants pulled down to about the middle of their butts, showing about half their underwear. I just read that, I think it was, the state of Alabama has now outlawed it as indecent exposure, with a third offence being a sex offender crime. As far as old men pulling up their belts to their tonsils, I suppose it looks ridiculous, it however does not look disgusting.
I don't know how it started, but nowadays in prisons guys feel that if their pants are the least bit tight, it means they might be homosexual. It seems to also have become almost trendy (although that may not be the exact word I want) to wear sagging pants.