One of the main dangers from E. coli infection comes from any open wounds, however small. As soon as the bacteria enter the bloodstream, then you're looking for trouble, especially if your immune system is out of whack. I wouldn't rub poo into a cut or scrape, even if it was my own poo.
E.coli that escapes the intestinal tract (ulcer or other exit) and into the body can cause serious complications, like peritonitis - which can be fatal if untreated. That is E. coli from your own poo.
Wikipedia states that most strains of E. coli are harmless, save for one particular strain that is very dangerous and can cause some nasty food poisoning (remember "hamburger disease"?), stomach acids or not. These strains release toxins that make you very sick or even kill you if your immune system is not up to spec.
The moral of the story is don't mess with E. coli or any other bacteria. It's like Russian roulette - the gun maybe won't go off this time, but every time you pull the trigger, you get that much closer to clearing out some space in your skull.
Even if your own E.coli is intimately acquainted with you, it can still throw you a nasty curveball.
Jenny.