This is disgusting. Come on man, you don't need to be messing with people like this. 

I have no respect for people that mess with the homeless. Seriously, what the hell is wrong with you. It is someone down on their luck just trying to survive. If I was homeless and someone was offering me a sandwich, I would probably run over too. Then you throw water on the man? Come on, that's messed up.

Good news, this employee has been fired for these actions.

My dad taught me something years ago. If I was walking near a fast food restaurant in the winter, I would go inside, buy a meal with a coffee and be sure I get a receipt. I would give the receipt to the homeless person sitting outside and tell them to go inside to warm up. Since they were a paying customer, they could stay in there for a bit. I always do this and it's just something to pass along.