Tip your baristas!!!
Tip everyone in the food service industry because there are more people involved than you think and everyone works hard. Even if the server is having an off day still tip. People depend on tips and you don't know what they are dealing with. If it seems they really are being unreasonable then talk to a manager calmly or ask for a different waiter or waitress. The rest of the staff who rely on tips shouldn't have to suffer if it is that one person.
The fact that i tip mine every single time, they have taken notice and started giving me free drinks, if they give you a free drink still tip!
Above all treat food industry people with the same respect that you would want. They are making your life easier and trying to make a living as well.