Tipping does have a dark side: It can be demanded, and shade over into bribery.

FORBES

College athletics now stands at a tipping point, on one side may be a revolution in the form of proactive social media education for student-athletes, on the other may be the largest suppression of 1st amendment rights in the history of this country.

FORBES: Manti Te'o Hoax Saga Tipping Point in NCAA Social Media Revolution

My only premium is the couple of bucks I slip the courier for each delivery (which I do just to be on the safe side, since I can find no mention of tipping etiquette in Kozmo's ordering FAQ).

CNN: Web shopping for the very impatient