I remember once when I was standing next to someone who was trying to get a screw in a light switch cover plate out with his knife. He looked at me and asked if I had a knife with a smaller blade. My answer was a resounding "No!" ... even though I had at least two in my pockets at the time.

And a few months ago my sister was visiting, and one of her friends joined us for a day out. Starting our hike in a local park, that friend noticed a tree where a bunch of idiots had carved their initials into the bark. She asked if I had a knife that she could use. My answer was "no". She thought that meant I didn't have a knife. It actually meant she couldn't use it.