To echo tptacek, I never had any serious issues, and I rode the Green Line a lot when I lived in Chicago. The closest thing to what you describe that happened to me occurred once, when I was waiting for a bus near Washington Park. Never on the trains.

I've lived on the other side of an alley from Austin, in northeast Oak Park, for 13 years, and no: I have never had an issue like the one you describe, nor has my wife and nor have my kids.