Recommended costume
Go to a wardrobe where you can change. Put on the school uniform then go to "Head". Switch it from nothing to the mascot head. By doing this you will get good compliments on clothing, and making out time with girls is reduced, which gives you extra time and the health bonus.
See the "Bitch" vomit in "That Bitch" mission
Hide in the trash can behind you after you place the stink bomb in "her" locker. When she does not see you, she will vomit and continue to do so as you make your escape. If she catches you before you hide she will run away screaming.