Wednesday, June 21 is National Selfie Day, which, aside from Thanksgiving, may be the most important day in this fractured and divided nation.

The selfie has only really been around since shortly after the turn of the millennium, but it has become as much a part of our way of life as breathing, eating and keeping up with the Kardashians.

Heck, the selfie was already an ingrained and (begrudgingly, to some) accepted part of our world when Ellen DeGeneres rode in and took it next level with the star-studded and now-infamous selfie at the Oscars in 2014. Nowadays, people will take a selfie in just about any situation (including by a passing train), which is just a way to stay on course, since data indicates the average person will take 25,000 selfies in his/her lifetime.

It's not hard to understand, then, why Twitter has been plenty busy with the hastag #NationalSelfieDay. Plenty of celebs got in on the fun, too, including Dwayne JohnsonLucy HaleMark RuffaloStephen Colbert and Shay Mitchell. Heck, even the Mona Lisa made sure to celebrate.

The Sexiest of Selfies: