It's an insulting term for scruffy looking people who are presumed to be homeless or drug-using.

The reason it's contentious is that one person uses it, someone else objects to it, people take sides along left-vs-right lines, and the thread devolves in to a shouting match.

I guess I meant the etymology of the word.

It seems it’s pretty well established though, from 2010:

https://www.urbandictionary.com/define.php?term=criddler