Goatse
There is a picture on the internet, you can find it surely if you look, of a man spreading his asshole completely wide open and fisting it. Its called Goatse as it was once hosted at goatse.cx.
Anyways it has since been removed, but the image lives on.
Now while I have no desire to spread that picture around the internet, disgusting as it is, I am sure that you can find it on google image search or elsewhere.
If you do look at it, you’ll probably have the same facial reactions that these folks did. This is a gallery of people viewing Goatse.cx for the first time and its fucking hilarious. Ron jeremy is in there. It even grossed him out.
Enjoy.