I've tried it, and it functions like a staining developer. It seems to be the tannins that function as the developing agent.

It also has the aroma of a grilled steak, which is a little peculiar in the darkroom.

It has been observed that tannins like catechol are present in human urine, but I haven't tried developing film in it.

So, you can use the coffee as a developer before or after your drink it

Okay, now we're just getting a bit too weird...

Does that make anyone wonder what coffee does to you?

Makes you a well developed person!

Didn't I read recently that drinking six or so cups of coffee per day will reduce your chances of developing (ooops, there's that word again) diabetes?

If that makes no sense to you, just wait awhile, and there'll be something else in the papers about the harmful/beneficial effects of too much/little (a) coffee (b) red wine (c) carrot juice (d) pyro (e) Ronsonol, etc., etc.
Come to think of it, anyone who relies on the papers for medical advice....

Automatic toning, eh? Well, I've "toned" prints in instant coffee. It doesn't change the image color, just the paper. Just kind of makes it look old and yellowed with age, sort of, which is what I was after. I highly recommend using coffee that has not yet been drunk.