the title and some of your wording has been pretty offensive to minorities, so expect a few impassioned responses. i hope you've recognized that you may exhibit some behaviors of your own that may effect your tips. my first boyfriend was tall, dark, thuggish, rough around the edges and the stereotypical gangster type that you yourself said you'd give less than your best service to. he's an engineer for mercedes so if you don't treat him like he's stupid for sagging his jeans he's likely to tip you very well. there are some people who wear suits and ties to work who are horrible people. there are some people who wear raggedy t-shirts and torn jeans that are the nicest people you'll meet. when you start serving EVERYONE fairly and not just people in armani suits with briefcases, you may find that 90% drop. i apologize if some of the responses have been cutting, but you open yourself when you imply that a certain ethnicity engages in wrong behavior, there are probably restaurants with all-white clientele that tip poorly.