It is also signals a package of personality traits: * rejecting other personal hygiene customs * being noticeably more pedantic * picking every battle/argume

It is also signals a package of personality traits: * rejecting other personal hygiene customs * being noticeably more pedantic * picking every battle/argument * lower than normal respect for other's boundaries * lower than normal awareness of how their actions effect others * making "being rational" a core part of their identity * dismissing human behaviors they don't do as irrational. usually these are the ones where rational explanations do exist, they are just difficult to re-invent on the spot. This package is common enough to have earned itself a name, which happens to be the easiest visual indicator.