The "other guy" routine used to hook me every time. I would get incensed at the notion that I was "behaving inappropriately" around other men and therefore teetering on the edge of cheating in his mind. Ppfft. what a crock of hooey!
Being nice to a man other than my husband doesn't make me a floozy. It makes me a human being! And these issues weren't mine, they were his. His insecurities and distorted thinking. His need to be "right" and "justified". It made his behavior ok in his mind...stalking me and hacking my email accounts and reading my mail and checking my phone logs and text messages. It was his way of rationalizing his own paranoia.
Yes, I could say ignore it. But I also know how it feels to be accused of something that violates my values in a big way, so it immediately sparked a defensive stance in me. I think there are appropriate times to GET ANGRY and tell someone off when they are being an a-hole.