If sex hair means what a girl's hair looks like after sex then sex mustache is what a mustache looks like after sex.
To a guy with a messy mustache: "Dude you have wicked sex mustache going on right now."

A mustache, post mustache ride.
by Emma Mara November 20, 2013
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Braiding your partner's pubic hair before giving them head.
Her pubic forest kept tickling my nose hairs because she didn't weedeat so I gave her a sex mustache.
by Phil Mahooterz January 10, 2016
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