LAUGH. IT'S BEEN SEVEN YEARS IT'S TIME TO LAUGH

Basically the anime is about this teacher that's extremely pessimistic if not nihilistic and who keeps "falling into despair" everytime he notices the bad in society, even for the tiniest things. Most of his class is made up of girls who all have very specific quirks about them. One in particular is his polar opposite, a naive girl who only sees the good in people and finds sometimes absurd justifications for the bad things that happen.

It's actually a pretty good anime if you don't like the typical stuff that you see most weebs drool over.

Anyway, the girl in the picture's quirk is that she wants everything to be precise and orderly. In an episode she said what's written in the pic: don't forget to laugh seven years from now. Today, it's been fourteen years since the episode was released. People who rewatched it seven years ago are watching it again, just so they can laugh and watch it again in seven years.