The last time I left home without a knife (I usually carry four, two of which are small fixed blades), I was in Jakarta, Indonesia, and I was worried about the metal detectors everywhere. I ended up getting into an inflatable air bubble that was floating on a pool of water later that day. I was with a whole bunch of gorgeous women (I was the only guy in the group) and one of the guys working there started messing with my baseball cap, which wasn't a big deal, but I was worried about the girls I was with while I was pretty much trapped in the bubble.
I thought I had my neck knife on, but I'd taken it off at the hotel before I left for the day. There was NO air exchange with the outside in the bubble (or it woulda let water in), which meant if those guys had decided to leave me in the bubble, I would have suffocated. It left me feeling incredibly uneasy. I was even more worried about my friends. Unless I'm on a plane, I will ALWAYS have a sharp edge on me from now on.