How big is your mustache? Does it extend so far off your face that is could either penetrate or physically injure your girl? It all depends on what we’re talking about here. If you're talking Santa Claus mustache, then get p right now and trim it. If you’ve got just an average, everyday stache going on, then you're good to go. Mustaches and oral sex go together like milk and cookies as long as you don’t look like Teen Wolf. Your girl won't even know it’s there.