Women in the 1920s who rebelled against conventional dress, hairstyles, and what was considered to be "ladylike" were commonly called

They were called flappers. It was somewhat derogatory because the the women were often considered to be promiscuous or lacking in traditional moral. They were basically something like women in skimpy outfits in clubs now, everyone in the clubs liked them and everyone outside thought them to be bad for the society.