Mincing is the act of putting mince/meat through someone’s letterbox during the night with the intention of it rotting and making their house smell foul.
Pieces of dead skin that reside on your chin because you have taken tablets to dry out your skin for extreme forms of achne. Can be used to decribe the "mince" or to describe a person with it. see examples below.
Person (without mince): Ya mince is lookin canny mean today.
Person (with mince): Shut the fuck up.
Person (without mince): MINCE! MINCE! MINCE!