Are you a Bruce Wayne on a budget with a crime to fight? If you have a few used up saw blades lying around, you can take grinder in hand and make yourself a few batarangs as you contemplate darkness, no parents, continued darkness, and more darkness.
This project assumes you don't have a metal bandsaw, plasma, laser or waterjet cutter, heat vision or any other method that makes hand cutting metal with a grinder obsolete. (We've been known to laser cut a throwing star or two.) The pleasure of this project is making something by hand.
Note: These can be made to be very sharp, so don't throw them at anyone. Cutting and throwing metal can be dangerous. Protect yourself. At a minimum, you should wear goggles. We wear full face shields whenever we work with the grinder or cut-off wheels, because although it's horrible to lose an eye, it's equally horrible to have a broken cut-off wheel fly into the side of your face. When we fight for justice, we wear spandex.