Pink Clothing
The use of pink clothing as the Plastics' coordinated outfit for Wednesdays exudes stereotypical femininity, but also acts as a militaristic uniform of conformity. At first Cady struggles to assimilate into this culture, wearing an awkwardly oversized pink shirt that contrasts with the rest of the clique. Eventually her clothing choices become seamless and it is Regina who fails to conform to the standards she previously reinforced. Thus the imagery of pink clothing helps assert the idea of conformity, while also tracking Cady's transformation into a "mean girl" herself.
Burn Book
The Burn Book has a paradoxical appearance of feminine pink tones alongside scrawled charcoal writing, reflecting the paradoxical nature of femininity as something that is both delicate and brutal. The Burn Book is a symbol of all the ill will that the junior girls at North Shore High harbor toward one another, revealing a host of secrets about the students and faculty.
Halloween Costume
Cady's terrifying Halloween costume makes her stand in stark contrast to every other girl at the party, highlighting her lack of social understanding during the first half of the movie. While The Plastics are primarily interested in projecting a sexually appealing image of themselves, Cady crafts a detailed costume with a clever punchline (an "ex-wife") that draws Aaron's admiration anyway. The costume reflects how Cady's individuality is more attractive to Aaron than are her attempts to emulate The Plastics.
Spring Fling Queen Tiara
Cady breaks up the tiara and distributes the pieces to the other nominees for Spring Fling Queen, and members of the audience. Cady's decision to shatter the tiara (which makes Damian gasp) symbolizes her desire to break up the social hierarchies that had dictated the lives of North Shore students. Rather than be part of an exclusive group that is idolized by the rest of the school, Cady offers compliments to a number of the girls in the audience, and forsakes the title of queen in the interest of bringing the school together on more egalitarian terms.
