Are you asking about inserting a bar of ivory soap in your rectum? Or like soaping up with Ivory and then fingering yourself or using it as a lube?
Naw, not me. I prefer the rounded objects, but have used soap to lube them up. If they are penis shaped, so much the better.
Many years ago, I had purchased a bar of soap-on-a-rope in the shape of a huge cock (10") for my ex-wife. She never knew I was using that soap more than she was, I'd fucked that thing down to about 7" when one day it was gone!