Basically, you can't. They are 5 yr olds who have gotten their hands
on some pretty sophisticated software that they use but don't
understand themselves.

using Fre Agent, you can select topics by Subject. This will list all
similar headers together. Recognising one, its' simple to delete the
rest, since they are grouped together.

Best approach ...NEVER reply [I'm guilty myself, I know, but will make
a new resolution to not do so.]

It deal with OT crap the same way since that's basically trolling as
well, and delete it out of hand. It takes only a few seconds with
practice. Now there are only about three messages left, but they are
worth the effort most of the time.