I'm not gonna make excuses for some people or anything, but when you hang out in chat a bit you learn who you mix with and not. Some people are simply there for social chat and they might bend rules, you learn who they are, if they are there and I'm bothered by them I don't join the same room.

As for excluding people, I really hate when it happens. Sometimes it's sort of by accident but if not it really sucks, I know. No one should be excluded or ignored IMO.