I think one of the aspects I like most about 3D printing is the ability for anyone to generate what I like to call a Very Specific Object, which is an item with a purpose so niche it's a near certainty no one but the author would ever have a use for it. Ergo, it's an item that by definition doesn't exist, or rather didn't until it was created for its bespoke purpose. And the point is that it does have a functional purpose, but the more obscure the better. The beauty is that we can create such things as we see fit.
I think I achieved nirvana with this, then, given that this model has garnered precisely zero downloads on Printables. Despite the fact that at least one or two punters inevitably download any damn fool thing I post there. Not even the scraper bots want this one.
https://www.printables.com/model/783183-ikea-nordkisa-drawer-stopper-clip
This is a clip-on end stop for the Ikea Nordkisa nightstand, in and of itself a specific enough object. It prevents the drawer from being pushed out the back, which is an aspect that while highly annoying has probably only had the chance to personally annoy a very, very small portion of the world's population.
My first VSO was a clip for this garnish/trim for some blinds my mom had. Due to the way the blinds fit in this specific window, my mom couldn't use the factory hardware to fix the garnish to the blinds, so for the longest time she was using adhesives which would fail over time. One day (shortly before my printer arrived) the garnish fell again and almost hit my cat, my mom expressed frustration over it, and over how she would have to go by more adhesives. I reminded her that I'm getting a printer, I could just make something that would mount it permanently.
My second one was two mounts for my IKEA lack enclosure. I wanted to make a Nevermore filter, so I needed a power supply. Thanks to working at an electronics lab, I managed to score the power supply from a server rack PC. It's absolute overkill for this, but it came out looking pretty clean, even modeled in a mounting hole for a simple toggle switch so I can activate the power supply without having to plug/unplug the unit.