Is it time to start calling out bad cyclists?

I really wanted to but I didn't want to come over as being condescending, should have suggested cycle training but that often brushes people up the wrong way.. What does one say in these situations? (serious question)

Well, the other day a girl was about to try to go down a gap of less than a foot between pavement and bus. I said, "That's a really bad idea," and when I had her attention continued, "people get crushed doing that." She stopped but at the next light, now with less than two feet she muttered, "eh" and went down the gap. sigh