BAD IDEA
I have a cup that is closed on top and open at the bottom. What should I do?
Congrats, you own a cup that can't hold anything useful. Maybe return it or just use it as modern art.
A cup closed at the top but open at the bottom sounds less like a cup and more like a prank or failed design. It won't hold liquid, obviously, so the best advice is to stop trying to drink from it. Either toss it, return it if possible, or repurpose it as a flower pot if you're into upside-down stuff. Otherwise, it's just a fancy way to waste your time and spills.