So, ok, there has to be a logical explanation, right? It must make some medical sense, right? Why else would all these people be spending all this money on coffee for their wazoos, right? Absolutely not! A Google search for the phrase "coffee enema" returns 61,700 hits. Maybe Freud was right about the whole "anal fixation" thing. A Medline search for "coffee enema"--using the extremely powerful, very user-friendly search engine relied upon by scientists all over the world--returned only fourteen hits, none of which were clinical trials on this subject. Two were unabstracted reviews criticizing the use of coffee enemas.
Overall, I'd have to say that is extremely compelling evidence against sticking a hose containing coffee up your own, or your friend's anus. It is my medical opinion that only a well trained provider of evidence-based medicine should ever have a crack (no pun intended) at inserting any thing in any ones' anus under almost any foreseeable circumstances. And even then, make them explain it to you twice, OK? Its your anus!
Now, having effectively ruled out the well-informed, "I've got logic and reason on my side" approach to this, we are left with trying to understand the other motivations for filling the colon with some quantity of Folgers, or Yuban, etc. If I could insert the sound of chirping crickets at this point, I would. It conveys absence, or silence really well. Close your eyes and picture it. Poignant, yes? Like most of this nonsense, coffee enemas are about money: profit margin. None of this is real science. Absolutely all of it is crap and belongs in the septic system with the usual contents of our collective colons.
Sites touting the use of coffee enemas often recommend them for daily use prior to other types of alternative medical treatments, such as liver "detoxifications," calling them safe and more effective than drinking coffee. http://home.bluegrass.net/~jclark/coffee_enema2.htm That's great. "Heres some nonsense to do that will keep you busy flushing coffee up you arse for a month prior to getting to the real stupidity."
The plural of anecdote is anecdotes, not data. No number of personal testimonials should be enough to convince a prudent, well reasoned person to flush coffee up his or her anus. Always hold any person who wants you to try something for your health to the same skeptical scrutiny that you would use when listening to your doctor describe the potential side effects of your prescription medications.