Black nail polish

Black is the only nail polish color that both genders like to wear. Girls wear black nail polish because it's such a bold and incredibly sexy color. Guys (cis) wear it mostly as a fashion trend statement (e.g. social media fad) or to symbolize that they are affiliated with a certain cultural movement (e.g. goth, emo). Only some guys wear it without any externally-motivated reasons. There is also a noticeable difference in HOW each gender wears it. Guys (cis) often do it hastily. They have no intention to fill the polish in completely, and prefer it chipped. Most would opt for matte black. This is likely to distance themselves from actually partaking in a feminine hobby, or to follow the trend. Thus for guys, it is only a means to an end. When girls wear it though, it will look unironically gorgeous and catches people's eyes. Most will get it done professionally, or do it themselves with unprecedented perfection. Girls will take the extra mile to use a base coat, and put a top coat over the black polish to make it nice and glossy. Girls also like their nails long and shaped. They'd look—as you'd expect—feminine. Guys rocking black nails isn't anything new or remarkable, but it would take some real balls (i.e. devotion) to paint them in a sincere impeccable fashion as a girl would.