Vest sold to the public are often a loose universal fit, so much like a tank top will come down and leave some of the chest area exposed if the vest he was using was just something he picked up at a flea market or an online supplier I can see how the bullet could "miss".

 

Guys a complete idiot, you want to test the vest? Put it on a watermelon damn, man.

 

Also keep in mind what makes these vest "bullet proof" is the metal plate inside the vest, it's completely possible he had the wrong plate in the vest and the shooter hit the vest but missed the metal plate.

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