Calvin Clackson stabbed friend wearing ineffective stab-proof vest EDMONTON, Alberta, Dec. 6 (UPI) -- An Alberta man who stabbed a friend in the chest as a test for what turned out to be an ineffective stab-proof vest was sentenced to six months in jail. Calvin Clackson, 21, of Edmonton, pleaded guilty Tuesday to criminal negligence causing bodily harm in the Oct. 15, 2012, incident that required friend Justin Harder, 18, to undergo emergency surgery for a bleeding chest wound, the Edmonton Sun reported Friday. The court heard Harder had been wearing a purportedly stab-proof vest and invited Clackson to test it out with a folding knife. "Unfortunately, the vest didn't work and the knife went through the vest and into the chest cavity and Mr. Harder was seriously injured," prosecutor Mark Huyser-Wierenga said. Provincial Court Judge Michael Allen said the stabbing was a serious incident that could have been worse. "It was foolish for the friend to offer the invitation," Allen said. It was criminally negligent for the accused to take up the invitation. "This is a serious event, this stabbing," he said. I don't care that the victim was stupid ... acting stupidly. This could have been a death.