It's when someone who has gone monumental sticks a finger up his or her ass in a public space and draws a fecal mustache over his or her lip, and then proceeds to act in a ostentatious and annoying way, often flirting.
Guy: Why has everyone suddenly left the dancefloor?
Girl: It's that douchebag dancing alone, he's pulled a Monumental Sanchez.
Girl: It's that douchebag dancing alone, he's pulled a Monumental Sanchez.
by AlabamaBaby April 12, 2016