anger management helps
...but sometimes the fuckers can really piss you off. I did the same thing. I bought this guy a donut and some coffee after asking me for change. He threw it on the ground and told me to fuck off. I really wanted to pound his face in at that point. I decided to never pay attention to them again they will always get the best of you.
I also see a bum around town that one time I drove by he was begging with a sign at the stop light. Really grungy looking old man looked like he just crossed the desert... I always wondered how the fuck did he get to this ( somewhat secluded spot ). I had to go back that way 10 minutes later and saw him getting into a very nice new model ford truck.