Mustache Dandruff
Granules of cocaine that have settled into the sniffer's facial hair, primarily in the mustache area. These can be formed from shakey hands, bad aim, or excessive nose hair which can act as a filter to larger debris.
Mikey must have snorted some cocaine in the bathroom because he has enough mustache dandruff to make Bobcat Goldthwait say, "I can't feel my face".