No, no, no. You got it all wrong!
Firstly, stingrays have no muscular control over their tail whatsoever. The only way their tail can fly up is if you step on them.
Secondly, stingrays are gentle creatures. They would never go on a killing spree. In fact, they couldn't.
Lastly, the tip of their tail does not have a barb; the barb is between the body and the tail.