Actors usually know what they’re getting into when they sign on to star in a movie, mostly because their lines have already been written down. However, despite being no stranger to improvisation, Jennifer Aniston was given some off-the-cuff dialogue that she wouldn’t say under any circumstances. As much as she tried to rebel against the “bullshit comedienne” image she’d been given, which comes with the territory when you’re the star of one of th…