Originally Posted by
rickair7777
I don't know what would happen if you told the FAA.
In a case like this, it would most likely be a he said-she said situation without definitive proof, but the FAA would most likely ask the certificate holder to voluntarily surrender their medical certificate. That does not mean that they would be obligated to surrender their medical certificate (because what if the accusations were false?), nor would it mean that their certificate would be revoked.
I saw a similar situation where many people felt that a specific pilot had a mental health issue and reported it to the FAA. The FAA only asked for the individual to surrender his medical certificate, which he chose not to do. He is still flying today.