Writers are magpies. We can’t help ourselves. If we see something interesting, we want to twist it into our plots, our settings, our characterizations. Weaving these things into story can often be safe. My extended family can’t help but notice little scraps of our lives turning up here and there in my books. In SUSPECT, for example, I obtained permission from one of my daughters to use her prom dress as a model for Jen’s. The basic uniforms at the Schoenhaus bear a close resemblance to the ones my other daughter wore when working at an upscale ski resort. But the comparatively skimpy maid costume came from my experiences of serving at a few weddings when they were short-handed at the college banquet hall where my brother worked. Those skirts really were so short that I didn’t even want to think about bending over. Those skirts were definitely designed for much shorter legs than mine. I’m just over six feet tall.
All of these examples are fairly harmless. But what happens when you want to model some of your antagonist’s qualities on people you know? The characteristic in question is so wonderfully sparkly. It would fit so beautifully with the plot. Well, then it really behooves the writer to give that character some extremely strong quirks or a much different set of circumstances so that your unwitting model would never recongize himself or herself.