In each airport, seemingly collecting dust, are small metal frames that show the correct dimensions for carry-on bags. I personally have never seen anyone (especially airline employees) use them to measure bags.
Much of the annoying aspects of airline travel center around the carry-on bag, and the side effects of the rules not being enforced. The poor people who are boarding last are pretty much resigned to checking their bag, even if their bag is the size of a change purse, because some other lout is hogging more than the allotted space.
Then there's the whole process of getting on the plane. You invariably stand in the aisle as someone attempts to defy the laws of physics to cram their pet elephant into the overhead compartment.
I have a simple solution: The Carry-on Cutter.
The small metal frames come equipped with saw blades that hack off anything that doesn't fit inside. If you don't submit your bag to the cutter, you have to check it. Maybe then people would realize that they didn't need 16 changes of clothes for their weekend trip, or that your relatives really don't care about whatever ridiculous junk you're toting back for them.
My brain is a curious thing. It bounces from place to place, from the exceedingly strange to the terribly mundane. Every once in awhile, something will pop into my head that is just completely out of nowhere. Totally random.