Light switch covers. One could be a face, and the switch is the nose.

Planets (half, anyway) that you mount on your ceiling or wall.

There’s just too many good ideas, and it’s hard to say what would be coolest without knowing you.

Since you posted this here I’m gonna go ahead and suggest glow in the dark cock rings.

3D print a brain to come up with your own ideas!

Glow in the dark filament is shit for glowing more than a minute. It’s like the cheapest toys you had as a kid.

But they illuminate constantly if you shine a UV (or IR?) LED on them, and you generally don’t see the LED light nearly as much.

So my vote is a bigger project with an LED in the base that keeps whatever you print lit up and looking spooky green for hours.

Ghost desk lamp with UV lights inside

Print a better post.