Gag gift.

edit: Apparently it’s for sewing.

It’s a French curve ruler. IIRC the original French curve was used for drawing and drafting, having multiple curves and cutouts. This was developed with the graduations and solid shape specifically for sewing.

Obviously dirty seamstress dick jokes as well.

My research shows that it was originally invented to check the wild claims of those bragging that they were larger than they actually are