I had an idea a while back for sewing Kevlar and thin wire (or maybe like a chain mail) into a leather jacket to offer protection from knives and other sharp implements.

Something like that always made sense to me, since the natural reaction when someone comes after you with a knife is to hold up your arms over your face in defense. With the bulk of the jacket protecting your torso and the sleeves protecting your arms (and therefore face) you're pretty much covered from the waste up. It wouldn't help with needles, or anything like that, but it would help with slashes and sharp edges; say, from a box cutter or flying shrapnel.