I think I have shared this story before on another forum. This not necessarily the narrowest thing my cat has perched on, but it sure was different.

Innocently I gave my very first cat a bath.
I had no idea he would hate it. He was so good but in a flash he was "perched" on top of my head. Not a scratch on me - but I was shaking taking him off my head dripping wet.
Later I howled with laughter at myself. What a sight for sore eyes.