And with that, Walter White vanishes into the desert—briefs, bare legs, mustache, and all.
And keep her away from magic markers unless you're ready for a mustache.
Whether this rule applies to the whole face or just the mustache region is a matter of dispute.
1580s, from French moustache (15c.), from Italian mostaccio, from Medieval Greek moustakion, diminutive of Doric mystax (genitive mystakos) "upper lip, mustache," related to mastax "jaws, mouth," literally "that with which one chews," from PIE root *mendh- "to chew" (see mandible).
Borrowed earlier (1550s) as mostacchi, from the Italian word or its Spanish derivative mostacho. The plural form of this, mustachios, lingers in English. Dutch slang has a useful noun, de befborstel, to refer to the mustache specifically as a tool for stimulating the clitoris; probably from beffen "to stimulate the clitoris with the tongue."