A noun. Slang for just about anything and everything you find confusing or disagreeable.

Maybe it's a southern thing. I grew up believing it was a popular phase until I used it in quantum physics lab. After calling the results of an experiment "happy horse shit" I was met by bewildered faces on everyone within earshot.

Example: "Well ain't that some happy horse shit?"
Example: after experimentally determining the speed of light to be approximately 47 mph -- "What the hell is this happy horse shit?"