I often read threads where people have had some stranger interfering, commenting on posters behaviours, actions etc. (You know the type of thread, strangers commenting on your shopping trolley, looks, weight, baby etc. etc.) And plenty of posters add to thread "just tell them to fuck off!" "Tell them to do one!" etc.
But do you actually say this in rl? What happens? Or is it what you were thinking but didn't actually do? I hardly ever confront, partly to keep my dignity, partly because I'd probably go overboard once started!

But I know some people say people should be more assertive.