Since we are no longer living in the 1970s, the mustache is no longer a glorious addition to a man's appearance. Instead, it has basically gone the way of the mullet; it is only appropriate for very specific people, and for very specific purposes. (Like being a pedophile, or playing the part of one in a movie.)
That said, there are certain men who can pull off the look and should never be discouraged from doing so. That's where this list comes in! However, if you are not one of these men, steer clear! (Seriously. I only want the best for you.)
First of all, men who have beards should feel free to add a mustache to their facial hair repertoire. It's only when the mustache stands alone that it becomes a problem!