I tip depending on the service but I am likely to give if I see the persons manager being a ass to them because nobody is lower than anyone else, management and customers who believe their have 'rights' need to learn this. You get your food or items, you eat and fuck off. Why over complicate that relationship with demanding a smile, false plesentry and all that bollocks?
I know some people will complain if the person serving them did not ask them 'how are you doing?' without sounding sincere. COME ON GUYS! Who really gives two shits about random fat arsed sobs wanting a greasy pizza or a can of beans? You sure as hell do not care about the poor sod serving you, why should they care about you? Fundamentally it is the price and items which people come back for, maybe the taste of the food, not how the over worked underpaid service wench forced a smile and asked 'how do you do?'
I hate the American service culture, it is leaking over here into the UK, cut bonuses, perks etc and demand more, gee. French have it right, take pride in their own jobs but take no shit from customers either.