Maybe someone can help us figure out how to do this properly.
I want to see the big ring it left in his forehead!
I does depend greatly on the "can" being used. If these are thin but "not" aluminum cans, the illustrated result will occur.
With an aluminum can it is easier, but you still do not "hit yourself" with the can, but rather "push it against and keep pushing until crushed".
One bit of advice: be careful as the can may buckle off center and you could potentially end up cutting of part of your face.