Ah! I haven’t really encountered this one in the wild much (vastly more familiar with “that guy has a bad hipster mustache”, luckily), but I see what you’re saying.
It becomes a bit more common if you are in an environment with certain kinds of ethnic makeups. It becomes an interesting case in as much as it is offensive at the expense of people who do not even have the trait. Ofttimes part of the conveyed insult is not just ‘you/your mother have a mustache’ but ‘you are of X racial background’. This means that people of race X who (or whose mothers) do not have mustaches are being insulted (as well as those who do).
The same principle, just with an extra layer of indirection.
It becomes a bit more common if you are in an environment with certain kinds of ethnic makeups. It becomes an interesting case in as much as it is offensive at the expense of people who do not even have the trait. Ofttimes part of the conveyed insult is not just ‘you/your mother have a mustache’ but ‘you are of X racial background’. This means that people of race X who (or whose mothers) do not have mustaches are being insulted (as well as those who do).
The same principle, just with an extra layer of indirection.
Huh. Our cladistics of insults could get pretty elaborate!