Toothbrush Fecal Matter
Explanation: Every time you flush a toilet, it releases an aerosol spray of tiny tainted water droplets. So if, like many people, you leave your toothbrush in the vicinity of a toilet, does that mean it's regularly bathed in bits of fecal matter? MythBusters Jamie Hyneman and Adam Savage uncovered the dirty truth to this myth by covering a bathroom with 24 toothbrushes, two of which they brushed with each morning — the others they simply rinsed every day for a month.
As experimental controls, the MythBusters kept two untainted toothbrushes in an office far away from the lavatory. At the end of the month-long trial, they sent their toothbrush collection to a microbiologist for bacterial testing.
Astonishingly, all the toothbrushes were speckled with microscopic fecal matter, including the ones that had never seen the inside of a bathroom. The confirmed myth unfortunately proved that there's indeed fecal matter on toothbrushes — and also everywhere else.