For Rachel, you need to be friendly with the Football boys to the point they show you the secret entrance to their hang out, and then just talk to Rachel a whole lot, eventually she will ask you about it, and you will tell her, she can then be found hanging out in the Gym in the evening, which leads onto the whole exhibitionism questline.Does anyone know how to trigger Rachel's and School bullies story?
For the Bullies, the best way to trigger it is just to keep walking up and down the corrodors in the school in the afternoon, each time you change location there is a chance you will have an interaction with them, it starts with them insulting you, stealing money from you, eventually they will drag you off to the changing rooms and force you to strip, it just gets worse from there on. If they are messing about with Cass (the redheaded girl), you have missed your chance and will need to start a new game.