So maybe you've been doing some home maintenance on your bike. Maybe you've fixed a flat, or dutifully lubed your chain. Now your hands look like this:
The grime that comes off your bike is a special kind of filth. It's especially tenacious and resistant to regular soap. I know, I wash my hands a dozen times a day. I use a heavy duty, gritty citrus hand cleaner, that comes in a heavy duty quantity.
But let's say you don't want to buy a gallon of heavy-duty, professional strength hand cleaner. One of my other favorites is Lava soap (it's made with pumice... get it?). Also gritty, and available in bar form at your neighborhood grocery store. It's not as quick as the citrus stuff and I think it takes a little more elbow grease to remove bike grease with Lava, so I like to pair it with a nice nail brush.
But maybe you don't have your Lava soap handy, or you hate volcanoes. In a pinch, you can use dish soap. WAIT! Don't wash just yet. To really, really get all the grease off your hands you have to scrub your hands with liquid dish soap DRY. That's the trick. Put the soap on your dry, bike grimy hands, scrub it in, then wash it off with warm water. You might have to go in for another round, but it works much better if your hands are dry for the first round. Trust me.
It's good to get your hands dirty every once in a while (or every day), but it's also good to clean them in case you want to have a sandwich or something.