A sexual act where a male ejaculates on or across the mustache of another male or rather manly female. The term derives from the mustache of the famous comedian, Groucho Marx, and the inherently sloppy nature of the action itself.
"Yeah dude, I totally gave that dude a sloppy groucho."
"You want it, don't you? You want that sloppy groucho. Oh yeah, beg for it, bitch!"