Well, as an example, last winter I had a "teenager" (young man) dressed in a heavy, long coat try to approach me from my blind side one night after midnight in a dimply lit, vacant parking lot of a convenience store. He came from the side of the building where he (obviously) didn't think I could see him. I was about 10 or 15 feet from the door when I noticed him approaching, and while he was about 15 or 20 feet away, I bladed my body to him, slipped my strong my hand up under my coat, secured a grip on my gun, and then while making the "stop" gesture with my support hand, I challenged him strongly with, "WHAT DO YOU WANT!". Caught him totally off guard. He stopped right there and asked, "you got a cigarette?". I said, again strongly, "NO. NOW GET AWAY FROM ME AND GET AWAY FROM MY CAR". He turned, walked out of the lot, and headed down the street. I never saw him again.
By challenging him as early as possible in the encounter, I was able to A) throw off his OODA loop, B) allow myself as much time as possible to assess, evaluate, and respond to the situation, and C) allow him an "out" before he went any further. While it's certainly possible he only wanted a cigarette, the "you got a cigarette?" line is one of the oldest tricks in the book for muggers looking for a way to distract you while they go about their business of victimizing you. Either way, I believe he realized at that moment that I wasn't going to an easy target if he had ill intentions. All is well that ends well.