Fun fact, in a lot of states even if they slam the brakes if you hit them you are still at fault. You should have been at a safe following distance, and no one knows what that actually means. People will argue that a distance of less than 2 seconds is totally fine and safe because they do it all the time. But a safe following distance means that at your current speed of travel if the car in front of you came to an impossibly instantaneous stop you should have time to notice and stop without hitting them.

At freeway speeds this is a minimum of 4 seconds following distance in dry condition. As in when the back of their car passes a sign that you should be able to start counting Mississippi’s and not reach that sign with the front of your car for at least 4 Mississippi’s

Now, if they come up from behind you swerve over and then instantly slam on the brakes obviously you’re fine(if you have a dash cam) there was nothing you could have done, but if you have just been riding their ass and then they slam on the brakes? You’re totally a fault as far as the law in many states is concerned