Mouse ears that attach to your baseball caps. It's comfortable and sits on my head well. I used this at a Halloween party as MIckey Mouse.

Print instructions

I used 2 4mm by 15mm and a 3mm by 60 for the center screw. I also used 3 washers on the inside of the hat to help secure it. Use 5% infill as it is a bit of a technical challenge to try to have the ears not fall due to their weight. If you do not have screws like mine I am sure you can add them yourself or drill them out.
I did this in PLA