>>5285473>>5285474>>5285495>>5285522The reason is that they are insecure. They are not confident enough to do a nice normal human smile, so they must look RANDUM AND QUIRKY AND CRAZY, its the only way they accept looking at themselves or being seen.
I actually caught myself starting to do it a few years ago but managed to stop myself.
You may notice the same concept with people sticking their tongues out or pulling general silly faces whenever their photo is taken.