LOL. I had to look that one up:
The National Park Service has a semi-private word for the above stories, they all involve, "tourons." Tourons is a combination of the word, "tourist," and the word, "moron." All though it is not clear where the word was coined, legend has it the expression started at Yellowstone National Park.
The web site where I found that has some great stories and one great picture (and one horrifying one).