Please don't call the police, that's gonna bring down a stuff storm on your family that I'm sure your parents don't even want. Also, IT'S YOUR loving SISTER. I would never in a million years call the police on my sister for doing something that doesn't hurt anyone. Calling the police will turn this situation into an over complicated nightmare. Just stop being a loving pusillanimous individual and accept the fact that your older sibling is going to drink a little bit.