I also agree that nothing screams "I'm a sphincter!" quite like asking for a 20% tip on a muffin, or a cup of coffee. Unless you physically came to me, got my order, and brought my food to me, you don't deserve a damn tip.
Another thing that restaurant owners do that is deserving of a throat-punch is to confiscate tips and dole them out to other workers, or divvy them up evenly amongst the servers. When I give someone a tip, it is because they've done a good job, and I want to show THAT PERSON my gratitude. I'm not remotely interested in helping the restaurant owner make payroll. That's not what my tip is for.
Tipping sucks and it is grossly abused throughout the restaurant industry. I'd be happy to see it die a deserved death.