The subject of what's a fair tip is, well, a fairly touchy subject for some people. CreditCards.com helps shed light on at least two interesting groups: Republicans and Democrats. Men, Republicans, Northeasterners, and credit/debit card users will tip at a median value of 20 percent. However, on the flipside, women averaged a 16 percent tip, while Southerners, Democrats, and people paying with cash came in at 15 percent. Finally, there are some folks who don't even tip at all. One in five people stiff their servers. The debate is now settled. 15-20 percent is the proper tip.