Honestly one of the biggest things people waste time on in the gym, its sad to see. When i was working as a fitness instructor at my local gym i used to constantly try to explain that sit-ups wont burn abdominal fat etc.
But people dont wanu listen! they're too tricked by the adverts of six second abs and the like!
Im a part of a band forum and there is an amatuer fitness thread thats been ongoing since Jan. Its insane the amount of mis-information that is out there and the shit people believe. One of the biggest ones is, spot reducing fat.