Unless you are a serial killer under FBI's protection like Hannibal Lecter, I don't think an amateur should try with inner tights. It shouldn't be quite that easy to pull off, plus the shock wouldn't be nearly as bad as when getting stabbed in the stomach area or the throat. So, if you fail with the tights, the opponent might not fail with their counterattack. However, a good stab in the stomach, and even if the target wasn't in an imminent danger of dying, there's still a good chance they wouldn't be doing anything but lying on the ground in agony. Whatever you do, though, don't try to aim at the heart. Chances are the ribs will either stop your blade or at least veer it off target.