Did you see that Craighill video? The one about pen clips?

Seems like that could be printed pretty easily.

Grab a wiregate carabiner or 10 and some mechanical pencils from your local billionaire and spend 10 minutes printing at 0.12mm layer height in PETG (or better — I used GF-PBT) and try it yourself.

In my opinion, it's not great. It won't deform when opened, sure, but it doesn't have a 'tooth' to grab onto what it's clipped around, so it slides off easily. Here's the Onshape link so you can modify the diameter to match your writing implement.

New version is a little more robust. You may need to scale up or down depending on how your printer is tuned.