My guess- It would depend on the situation. Actually it could be an infinate number of things: If you're throwing it at the homeless person to physically harm them for no particular reason it would be considered assualt. If you were throwing it at them to give them the money rather than harm them it would be charity. If you're playing catch with the homeless person it would be entertainment. If the homeless person was walking towards you with a nail ridden 2x4 with the intent to end your days at redhotpawn it would be self defense. If the homeless person was on television and you were throwing it at their televised image it would be stupidity. If you were the homeless person throwing the money at yourself it would be self loathing or treating yourself depending on how you look at it. If you missed them it wouldn't matter what your intention was, it never would have taken effect. My guess would be that your question has many viable continuations, and only under the absolute definition of your terms could you contain your question to the conclusion of charity vs. assualt.
+1 Assault. When you throw anything at anyone it is at least impolite and is showing you being disgusted with the person himself, or with something that he's doing. If you don't like them - just don't pay. In the end - it's only your choice.