Under anal intercourse, put your finger up her anus, then draw your finger over her upper lip, giving her a brown stripe resembling a mexican revolutionist mustache. Thus "Dirty Sanches"
When one sticks index finger in or around butthole and walks up to an unexpecting victum then rubs saturated finger between upper lip and nose area.
Boy 1 "Daaang girl did you hear what happend to Gina?!"
Boy 2 "Naw, son what went down?"
Boy 1 " Girl Gina was actin a fool so Shawndra stuck that finger of hers in her booty hole and gave Gina that dicklessdirty sanches!"
The act of sticking your entire face in your lovers ass and dismantling from left to right then squeezing the ass checks together with your facein the middle forming a sandwich.