As airlines keep packing more passengers into their airborne sardine cans, the space between rows in the cheap seats section gets smaller and smaller. And when the passenger in front puts his seatback in recline position, it’s painful to those behind it, especially tall, leggy ones.

If you’re having space invasion problems while flying, check on such devices as the Knee Defender. They’re plastic, foldable and easy to apply in front of your seat. Of course, you may first politely ask that the seatback not be slammed suddenly into your vulnerable kneecaps.

Or you can be just as mean as the seatback pusher and apply the device secretly and securely when you first sit down. Then enjoy the classic scene of the pitiful pusher suffering Sisyphus struggles.