Bonus points for being a RBM to somebody else's kid!
Not my kid. He was playing quietly in his room. No, it was our neighbor's daughter, who really is a perfectly nice girl. But her mom was either out of earshot or ignoring her on purpose. So the daughter did that thing that even the best kids do sometimes. She called, "Mommy!" And then, when that elicited no answer, she called again, in exactly the same tone (and volume, and tempo, and everything else), "Mommy!"
I'm not completely evil. (Really.) But the thing is, because of the way our apartment is situated, we get a lot of noise from this family, and they get very little of ours. And as it happens, my white-noise machine had just died. So had my clock radio's CD player. So I had none of my usual defenses.
I can tune out a fair amount. But she just kept saying it. "Mommy!" Pause. Pause. "Mommy!" Pause. Pause. Not just a couple of times. My computer's clock logged in five minutes of this, while I gritted my teeth and tried to work.
I don't know which was worse: that the mother was just letting this go on and on and on (if I can hear it in another building, I have a hard time believing that the mother in question could be genuinely oblivious), or that the little girl's mental logic was apparently along the lines of, "Hey! This didn't work the first four thousand times! Instead of moving closer to the person to whom I'm speaking, changing my wording in any way, or just getting on with my life, I'm going to say the same thing again! And again!"
After five minutes of "Mommy!" "Mommy!" "Mommy!" had elapsed, I knew that this wasn't the real world. I'd died without noticing it and been sent to a very personalized Hell.
I couldn't take it any more. My window was wide open. I used to be an improvisational street actress, and I have some training in projecting my voice.
The next time the little girl said, "Mommy!" I belted out, "ANSWER HER!"
There was a stunned silence.
And then I heard the little girl saying, almost to herself, "What the...?"
The worst part, so far as my RBM status is concerned, is that a minute later I had to go down the hall to get something. As I passed my son's room, he gave me a look that told me just what he thinks of people who set a good example to their tender young offspring by bellowing out windows.
"Um, did you hear that?" I asked, a little sheepishly.
He cupped his hand to his ear, as if he'd been stricken deaf by my shouting. "WHAT?" he asked.

Real Bad Mommies