If you quickly raise your weapon and aim around +/- 20° from the horizon on vertical axis, and shoot, you'll shoot yourself with your weapon. ( looks like in the chest)
[You need to quick tap, aim and fire]

If you spin quickly and fire in any direction, you'll shoot yourself. [also with the quick tap]

If you hold fire key on auto weapon and quickly spin around you'll shoot yourself again. ( problem when multiple zombies or wolves surround you and you need to spin and shoot quickly)