I was sorely disappointed by her looks in the video, but more importantly, the story line also bothered me. It didn't take me long to realize why...
After apparently being cheated on, Katy Perry dumps her boyfriend (which is smart), and then decides to overcome the emotional pain by cutting her hair, joining the military and being "tough" and independent. I am hoping the not-so-subtle message of the video is less catchy than the song (which is still stuck in my goddamn head...), because it essentially says "if you are hurt by a man, an appropriate and liberating response is to de-feminize yourself."
Nothing could be further from the truth. No reaction to rejection will damage your chances with other men more (especially if you cut off your hair like she does in the video). A woman who responds to rejection by becoming more masculine is like an athlete who responds to a difficult loss in sports by intentionally injuring himself or skipping trainings and practices - it is absurd. The athlete damages the body or lose the skills that made him a competitive athlete in the first place, just as like Katy Perry throws away the disposition and looks that attract men the most. She gains her personal independence at the expense of attracting men. That is to say, by throwing away her femininity and closing herself to male companionship, she sacrifices the potential for long-term happiness in a good relationship (however difficult it might be to find) for the momentary happiness of personal "liberation."
When a message like this is surrounded by a catchy song and a flashy music video with a famous celebrity, it is inevitably romanticized, and the message can be difficult to divorce from its medium. Be careful about getting sucked in.