I believe that the reason Marjane purposely wore this in front of her teacher is almost unexplainable. Marjane is a teenager this far into the novel, and teenagers do some of the craziest and dubious things. Why would someone smoke a cigarette? They are only proven to be bad for your health in multiple ways, as well as addictive, so why would someone purposefully put such bad substances into their body? It is because as a teenager, Marjane is trying to figure out who she is. She is trying to be unique but doesn't necessarily know how, so she is attempting new ways of living life to see if she likes it. Whether Marjane wears something that is clearly against her country's beliefs and practices, or listens to rock music in her room loud enough to shake the building, she is just trying to find out who she is through trial and error. She commits herself to these crazy things that only a teenager would do, like force herself to smoke a cigarette even though she absolutely hates the taste of it.
As a teenager, Marjane is trying to be herself which means breaking off from society at times. She wears a Michael Jackson button on a jean jacket in front of her very strict teacher. By attempting to be herself, she gets punished. By trying to break off from society, she gets pulled in deeper. Being a teenager in a society like the one surrounding Marjane is very restricting, you can not find yourself when dodging and ducking under boundries.
