A man wears an earring in whichever ear he pleases. At one point in American history, there was supposedly an encoded message about sexuality contained a man's choice of the left or right side, but today, having an earring on either side means only that you have a hole in your ear.
The notion of the 'right ear rule,' in which heterosexual men pierce only their right ear and homosexual men pierce only their left ear, may have originated in the 1970s. At this time, other fashionable forms of coded messaging about homosexuality were also in use, such as the "handkerchief code," wherein gay men wore different colored handerkerchiefs in their back pockets to indicate different sexual preferences. This system of encrypted messages enabled gay men to find each other while going unnoticed by those who might judge or oppress them.
The rising visibility and legitimacy of gay and lesbian populations in the U.S. has rendered most of this coded communication superfluous, and now men off all sexual orientations choose to pierce or not pierce their ears in whatever manner they like. However, the so-called "right earring rule" may still prove useful in rural or isolated areas, or parts of the world where homosexuality is culturally taboo or even forbidden by law.