Guys get mad at their girls when other dudes hit on them or are nice or friendly or flirt even if they know the girl is in a relationship, but then why do they absolutely hate it when their girlfriend does it back to them?
Both genders really get mad for being like the same exact people that flirt with their partners..
Because it is not the same people doing it. The loyal partner in the relationship has a legitimate reason to be upset if their SO is being disloyal and flirting with others.
by the way, it IS disloyal to post provocative pictures online when in a relationship because they are purposely looking for attention from others outside the relationship.