A gentleman's hands should be clean. That's just good manners. Nobody wants to shake hands with the guy with dirty fingernails or worse, the guy who rationalizes why he needn't wash his hands after using the bathroom. And manners aside, making sure that you're washing your hands regularly (and correctly) will ensure you escape cold and flu season unscathed.
Of course, even if you are washing your hands, there's a good chance you're doing it wrong. According to Dr. Elaine Larson, dean of research at Columbia University School of Nursing and renowned hand-washing expert, the biggest mistake we make is not covering the surfaces that we are most likely to touch, which are actually the fingertips. People—men especially—quickly rub their palms together, when the fingers are the most critical. You see, it's the fingertips that touch your face (the eyes, nose and mouth) unconsciously all the time so that's what you want to make sure you're getting clean.
Run them under water (hot or cold doesn't matter), apply some soap, then work it into a later. Make sure to scrub the backs of your hands, between your fingers and under your nails. They suggest scrubbing for a full 20 seconds, but if you hit all those spots, you don't really have to worry about timing it. And when you don't have immediate access to a sink? Get yourself some alcohol-based hand sanitizer. Unlike soap, which washes the germs off your hands, sanitizer actually kills the germs. According to Dr. Larson, a ten-second application of alcohol is the equivalent of a five-minute hand washing.