When your router stops working
How are you supposed to watch Himouto! Umaru-chan if you can't even connect to the internet? You might as well be back in the Middle Ages.
When a pushy guy/girl just doesn't get the message
When your suitor just doesn't get that you're just not that into them, that's when a true friend will suck it up and help you chase them away. Even if it means enacting Romeo and Juliet. The "Sorry, I have a boyfriend/girlfriend!" excuse has never been more flawlessly executed as in Golden Time.
When the person you're trying to reach isn't home
Just kidding-with cell phones, instant messaging, and SNS websites, this should never be a problem. Unless you live in a giant harem of beautiful aliens, like the girls of Sekirei, of course.
When you press down on the wrong side of a mechanical pencil
Who needs railguns when you can pierce all the planets by pricking your finger in Nichijou?
When you can't cook
To cut something, you just stick it with the pointy end, right? Shiina from Sakurasou no Pet na Kanojo is a yandere in the making.
When you meet your favorite celebrity
When you wish you were rolling in cash
We can't all be rich like Mugi from K-On!, but most of us dream of the things we'd buy if we were. Then there's people like Yui, who dreams of getting slapped with cold hard cash. But hey-to each their own.
When you have FOMO
We've all been where Yato from Noragami is. But sometimes you just have to take a step back and let your buddy have some space, ya know? Otherwise they might punt you into a lake.
When you can store things in your bra
Sure boobs are awesome, but bras are not the most comfortable thing in the world. One of the few pluses, however, is that if your chest is large enough, you can treat them as extra pockets! Cell phones, cash, even Exceed from Fairy Tail!
When you need to up your poker face game
On second thought, if you're like the girls of Nisekoi, maybe it's just best if you wore sunglasses and a face mask.