This time of year, every server dreads the return of the students to the city. Look, I understand that you are living on a budget, I'm a student too. However, that doesn't mean that tipping etiquette doesn't apply to you. Consider the tip as part of the cost of the meal; if you can't afford that cost then go get some fast food.
Servers have to tip out to the kitchen as well as other support staff, in many cases about 5% of their sales. That means that when you don't leave me a tip, I am essentially paying to serve you. Sorry to single out students, there are plenty of other assholes that don't tip either. —I don't want to pay to serve you