One in ten people have a third nipple. Most are mistaken for freckles or moles.
That's a pretty high statistic.
I am suddenly very aware of any mole/freckle/blemish on my chest.
Check out the article on triple nipples on Wikipedia. Nice to know that famous, good-looking folks like Carrie Underwood and Mark Wahlberg suffer from this all-too-common disfigurment.