“Wait, I thought I was watching a romantic comedy, not a murder mystery…”.
Don’t panic! Here is the explanation:
This particular action is called: 壁ドン (“kabe don”) which literally means Wall (壁) and a sounds of hitting (ドン) (yet another onomatopoeia we shall discuss it at a later date).
Believe it or not, it is considered a good thing – something of a romantic gesture in Anime and Manga – but the origin of this expression is a bit more mundane.
In the past it you would 壁ドン if you had incredibly annoying and noisy neighbors. You would literally hit the wall to let them know that they are being too noisy. For the purposes of this blog entry, the action can be taken to mean asserting your point (in this case, making sure the romantic interest of your choice is aware of your intentions) by slamming your hand onto the wall next to their head. Don’t try this at home, kids – it’s actually quite intimidating and confusing when practised in real life.
So next time you are reading a Manga or watching your favorite episode of a beloved anime and encounter 壁ドン, don’t worry: it is a romantic gesture after all.