I want break my arm/wrist?

I am not a phsyco I do not have issues but today I smacked my arm/wrist off a desk accidently but I got sent home and my team leader dident belive me he thought I was faking. I was thinking if I acctually broke my arm and came to school with a cast on then he woulf acctually learn to belive me. So could you tell me ways to brake my arm.