If approached by one of these "I'm broke" guys, you could always reach for your cell phone and tell them "Let me call the police for you. I'm sure they will be glad to help". That would probably make them scatter quickly.
Unfortunately, I doubt that will work. IMHO, 1) the guy probably wouldn't care 2) The cops probably won't even show-up 3)He will then know that you fear him and will become more aggressive.
Best thing is to stand-up to them and just ignore them. They don't want to fight ... they just want an easy hand-out.
I had one acost me here in El Paso out in front of best-buy one night. He was extremely aggressive and was borderline violent. He approached me after intimidating a woman in a car into giving him money and I told him to "F***-off". He became more aggressive and continued to hound me. I said, "I am only going to tell you one more time ... "F***-off"! He continued to hound me saying that he wanted to talk to me and I became enraged and said, "FINE! You want to talk to me?" I charged him and said, "Then come here you [expletive]!" LMAO, he couldn't get away from me fast enough after that!