giving a tip is like a slap in the face to them if u go by the "theyre getting minimum wage" theory...its like ur saying "take this change and buy ur own donut u peasant"
a tip I always thought was to be given for someone going out of their way to assist/help you...giving great customer service etc...i doubt thats happening in dunkin donuts frequently...they give u ur coffee and u keep it moving

I believe that if you do good things for other people good things will come back to you