Until mental health issues hit you or someone you know well, it can be hard to be empathetic to people suffering from them. To this guy it may not have seemed wrong or inappropriate – a person’s brain can be sick or damaged just like their heart, kidneys, etc can be. A large percentage of the homeless population in the US is made up of mentally ill people. What you were serving likely would be the only food he would get all day – while you and your sister likely had 3 meals that day. You generally don’t need to serve free meals to people who are capable of caring for themselves, this is exactly the kind of person who needs the meal services you were providing. If something like this happens again, do your best to be accommodating and don’t lose your temper. If it is a situation you really can’t handle, ask them to please wait while you get an adult.