I second the knife with the little glass breaker nipple on it. As resident manager of a “treller park” in North Carolina, my brother carried one of these and demonstrated it to me one day when I was visiting. One of the residents of the park, an excitable fellow highly reminiscent of Earnest T. Bass, clad in jeans (just jeans, no shirt, socks, or shoes) presented himself at my brothers door. The fellow had worked himself into a lather, possibly with the help of alcohol and various controlled substances, over some personal affront that he blamed on my brother. Electricity cut off for nonpayment or something like that. The agitated gentleman was making an uncomfortable scene on my brother’s mobile home steps. My brother very nonchalantly opened the screen door, reached out and tapped the protesting fellow right on the crown of his head with the glass breaker on his pocket knife. Just a little tap, but the methamphetamine afflicted gent went down as if struck by lightning. So, I have to conclude that a knife so equipped can be quite useful for resolving certain unpleasant encounters.