The tip of a sharp knife is capable of applying a surprising amount of energy to a tiny target area, and the sharpness and hardness of a knife blade can frequently defeat the woven fibers of bullet-resistant soft body armor. Most bullet-resistant body armor is better at stopping a 9mm than stopping a 6″ hunting knife.
I know that you only live once, but wearing body armor strikes me as more than a little paranoid unless you’re a soldier or police officer.
If I had to go in harm’s way I’d happily endure the bulk, weight and sweat of bullet- and stab-resistant armor. But I’m pretty sure I wouldn’t trust my life to any vest that cost less than a single green Benjamin. You?