First of all, if it's not important enough, and you don't believe it enough to own it, as in put your name on it, it's not important enough to talk about, periord.
Second, have you brought this up with the person in question and tired to resolve your concerns?
If you're willing to put your name on it, and if you have spoken to the person in question about your concerns, if you HONESTLY believe that this person poses a threat to others and they are unwilling to stop whatever it is they are doing, well contact your FSDO
https://www.faa.gov/about/office_org/field_offices/fsdo/
That said, the only situation I could think of that you wouldn't want your name on this, would be if you're not comming from a honorable position on this thing, and might be worried about a justified lawsuit or old fashion ass whoppin for making trouble for someone over what you know is really nothing, I hope that ain't the case, but if you're going to be putting someone's ass in the fire, have the honor to own it.