Tubgirl

Tubgirl is an extremely offensive image of a chubby (Japanese woman in a bathtub squirting excrement into the air, like ment?)os being dropped into a coke bottle, as it falls on her masked face. The orange color of the liquid suggests it may be enema fluid or even orange juice rather than feces per se.
She appears to be wearing a super hero mask and knee high socks. Additionally, she is laying on a silvery sparkle bath mat.

Origins

Tubgirl is not as well known as some other shock sites such as Goatse and Lemon Party. As such, there's less research as to her origin. It is likely that she is Japanese, or at least the picture is, as the vulva is censored. Japan is one of the largest producers of pornography, and is known for having laws restricting the explicit depiction of genitals.

Current status

Tubgirl is still quite easy to find on the internet. Like many shock sites, she is often linked to people under false pretenses. An example would be advertising a link as a picture of a dog. Note that this is currently illegal.
Images were the original shock sites, but have since branched out into loops (.swf or .gif), videos, and code that exploits the browser. As such, tubgirl is not used as much as it was before.