This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Afro Samurai
The whole idea of a person having a headband trying to kill another person that has a headband that shows that person higher social status than the other.
Not only that, the Number One headband is held to make the wearer a god. This motivates people to endless murder and atrocity simply to possess the Number Two headband, which is required to take on the Number One. Afro's whole life revolves around these two mundane things, thanks to people obsessed with the whole system. Society in Afro's world is fighting and killing countless innocents over a mere superstition. There's little evidence to suggest that these headbands are more than just pieces of fabric, which Shichiguro lampshades later on in an attempt to convince Afro not to kill him for the Number Two Headband to no avail.