I guess this little thing prevents the seat in front of you from reclining. Denver to NY flight was diverted to Chicago after an incident where some dude used these. They come with a nice explanation card to hand out. http://m.bbc.com/news/28942485 That thing is probably one of the most obnoxious things I could think of. Flying is such a hassle as it is, now you have scumbags preventing people from reclining their seats? I guess the lady dumped her cup of water on the guy.