When you really really want to emphasize that no one cares about something. Not only does it feel satisfying to say, it's a quick and easy way to shut someone down when they say something stupid or trivial.
Guy 1: My favorite color is white.
Guy 2: No one gives a shit.
seriously no one gives a shit about anything you post about urban dictionary on your story
no one gives a shit, stop fucking posting these annoying ass screenshots