If you're ever stuck in traffic on a busy street, check the solo drivers in the cars around you. I'd guarantee a good percentage have their gums flapping. Now they might be singing along to the music or talking back to Siri, or Bluetoothing on their cell phone, but I bet the odd one is saying something like, "I must remember to pick up the dry-cleaning on the way," or "Gosh darn, I forgot to take the chicken out to defrost," with no one but themselves to hear.
Hearing your dialogue spoken can sometimes help if you're trying to make it sound right in a story you're writing. I found it's best first to open your door, look right and left and then close and lock the door before warbling aloud your written words, especially with the reciprocal nature of dialogue. Someone passing your door might get the wrong idea.
There is a fine line between the occasional spoken self-admonishment and the continuous stream of words that makes the other mall walkers figuratively pull their skirts aside and pass to the other side of the concourse to avoid you.
Sometimes I think my family believes I'm teetering on that line. I've found the perfect answer for them when they ask, "Mom, are you talking to yourself again?" It wouldn't have worked a few centuries ago when it might have brought out the torches and the pile of burning faggots, but it works for me. I just answer, "No, I'm talking to the cat."