Caitlin Cook wrote an entire musical based on quotes she found scrawled on bathroom stalls.After college, the art history major grew tired of how pretentious that world could be, and became fascinated with bathroom graffiti.“I loved the idea that if you take all that elitism away, you just have people trying to communicate with each other,” Cook, 33, told The Post.She first found inspiration in a dive bar in Chicago: “Writing on toilet walls is neither for critical acclaim nor financial reward. It is the purest form of art.”Thus began her 10-year search for quotes scribbled in restrooms in places like Australia, New Zealand, Vietnam, Indonesia and Iceland. In women’s bathrooms, she often finds “gossipy, fun” dialogue and empowering notes.