I was told by the police to throw water on people in this situation. It's not considered assault and it gets them to leave. In certain places police won't show up for stuff like this so you have to deal with it yourself.

I have no idea what the back story is behind this so I can't say whether this was warranted or not, but I can say that I've had to deal with some pretty awful homeless people before. It's easy to say that everyone needs to be treated with respect, but it's a lot harder the 20th time you've had to clean up dirty needles and shit stained walls. A homeless man once attacked me with a shovel for waking him up while I was cleaning a parking lot. We need better options for the homeless and a better safety net to take care of them, but we shouldn't expect the bottom of the pay scale employees to have to deal with them.