Put a hole in a beer bottle cap.
Leave the bottle cap on the bottle.  Use a nail the size of the hole you want to create.  Pound the nail through the cap and into the bottle with a hammer.  Remove the nail.
Place a bottle cap onto a piece of wood so that the flat surface is down against the wood.  Use a nail the size of the hole you want to create.  Pound the nail through the cap and into the wood with a hammer.  Remove the nail.