Why do people insist on making dumb faces in their Facebook pictures?

The peace sign pucker lip; the dumb surprised face with their mouth in an O; the gritted teeth face; the picture where you point at the person next to you; or people who go out of their way not to smile and make a fake mad face. Do they really think it's cute, I personally think it's juvenile you'd out of your way to twist your mouth in these positions for a picture. Just go natural.