According to several reports, Joaquin Mendez (23), from Florida in the US, and his cousin were at home last weekend when the incident happened.
The deceased is said to have wondered out loud if the old vest was still working.
His cousin Alexandro Garibaldi (24), reportedly pulled a gun and said, "Let's see."
Police arrived on the scene several minutes after the shooting. They found Joaquin outside with a gunshot wound to the chest.
Alexandro initially told the responding officers that her found his cousin wounded after hearing a gunshot. But his story was disputed by a witness revealed how the pair had intended to test the vest.
Joaquin was rushed to hospital where he died from his injuries.
Alexandro has since been charged with manslaughter.
Sources: wfla.com, metro.co.uk, wesh.com