Chair rails
It’s not that chair rails are bad. In fact, they serve an excellent purpose: to stop dinner guests from going too far back in their chairs and damaging your drywall. However, chair rails can make a room look more cramped than it actually is. If you want to add more space to a room without tearing down and rebuilding its walls, just remove the chair rails.
Truth be told, chair rails have never done anything ever. They serve a noble purpose, but taller chairs can end up punching a hole in drywall anyway. What you should do is not invite clumsy guests who lack a feel of his or her surroundings.