Ugh, don't get me started with that. Even people who I consider intelligent have made this mistake. Part of the problem is that the video fills the phone screen so it doesn't dawn on people it won't "fill the screen" elsewhere. I feel like the phone manufacturer should somehow shrink what's on the screen when it's in portrait orientation to drive that point home and prompt people to rotate the phone into the correct position.

I see this all too often. And Snapchat made it worse, even though it will reorientate the screen for the video when you turn it. But since it keeps it video contained in it's app (for the most part, although you can save it out to your camera roll), it's not as horrible as seeing the black bars and portrait orientated videos uploaded to YouTube and other video services.

This guide should be shared with everyone that uses a phone to take video.