Have you or anyone you know used vicks vapor rub to clear dark toenails? Do it work?

It depends on what is causing the "dark" toenails. If they are sort of green and flakey then it is a fungus. The most effective treatment is a pill you take for 6 weeks from your doctor (griseofulvin). Otherwise the Vicks can work (it just takes a good month or two and a lot of dedication to apply it twice a day). You can also try soaking your feet in a mild bleach solution (1 part bleach to 10 parts water) once or twice a day for several weeks. Some people have had luck with a mixture of 1/2 and 1/2 vinegar to water and soaking once or twice a day for several weeks. If your nails are just really thick and dark from constantly hitting them against your shoes (runner's toe), then you need new shoes.