Honing rods in the kitchen. People always try to use these to sharpen their knives but it never works and when their blade that’s dull as a butter knife isn’t any sharper they have a big hissy fit about it.

Most chef knives will form a burr (a deformation at the edge), even if sharp or very sharp, and this burr will reduce the cutting performance and it will feel “dull”. You don’t need to sharpen the knife again, it’s still technically sharp so it is honed instead. The honing rod’s grooves will realign the edge and the knife will be “sharp” again.