A cathartic satire. I need to remember to have this on hand for the next time someone sends me an e-mail with any of these ridiculous apocryphal stories.
It is unclear whether all the readers are familiar with the ubiquitous chain e-mails that this is parodying.
So here they are:
Atheist Professor vs. Chalk.
Atheist Professor vs. Einstein (if you scroll down, this one also has the marine story and an especially nasty and hyperbolically silly variation involving a Navy SEAL.)
For a bonus, here is a fun cartoon on the chalk story.