Waste Not, Want Not
This is just plain rude. This person found an essentially empty milk jug sitting in their refrigerator. Their roommate left just a tiny droplet of milk that could’ve easily been poured over a bowl of cereal or consumed in a second. We’d understand if there was enough in the gallon for at least one bowl of cereal or a cup to drink. But that’s nothing.
If we were reaching into the refrigerator thinking there was enough milk to pour on our cereal only to be greeted with this sad display, we’d be irked too. It’s wasteful, not to mention annoying. Just use the rest of it, then dispose of the jug like the rest of us. It’s not difficult to do.