First in leotard etiquette is that you can wear a leotard if you are appearing on stage. If you are dancing, in a ballet, part of an opera, or doing performance art, you can wear a leotard and you will be fine. If you are a rock star, you can wear a leotard in only a couple of situations: if you are a woman or if you are an 80’s hair band lead man (see Poison, Twisted Sister, or Abba). A basic rule of thumb, though, is that if you are on stage performing, you can get away with a leotard.
Secondly, when it comes to leotard etiquette, keep in mind that a leotard is never okay if you are severely overweight or obese. When little is left to the imagination, you can end up painting a picture nobody wants. If you are a man, this goes double as you are put on display at a level that is beyond description. In fact, when the leotard actually debuted in the 19th century on a French trapeze artist, it is said that many came to see the outfit and what it displayed more than the act itself.
Thirdly, leotards are okay if you are a super hero or playing one for Halloween. Superman, Batman, and many other comic book superheroes made the leotard okay. Its sleek tight fit make for a great outfit when fighting crime. No extra fabric to get snagged and nothing to resist wind as you fly or run at the speed of light. If you are going the super hero route, however; you must make sure you wear proper boots and cape to complete the ensemble. Also, superhero leotards should always be worn with bikini briefs over the top. Heroes are modest.