I agree with Dr. Ralph, additionally I would say to be aware that your underlying assumption (that they are talking about YOU) is very likely incorrect in most cases. Whenever you notice yourself ‘on guard’, take a second to realize that you don’t have any firm reason to suspect that you are being talked about. Unless you have firm and clear reason to suspect that they are discussing you, immediately let it go.
If you get your guard up whenever you think someone ‘might’ be talking about you, 1) you end up on guard and stressed out needlessly and frequently, and 2) you draw attention to yourself. If you can keep in mind that it is very very unlikely that they actually are talking about you, then it’s better for you, the way you feel, the way you live, and the way others view you if you let it slide on by without reacting.
If they are talking about you 1 out of 500 times that you suspect that they are talking about you… I’d rather accidentally not notice that they are talking about me 2 out of 1000 times than to incorrectly assume that they are talking about me 998 out of 1000 times. That incorrect assumption could get triggered often enough to leave me exhausted from being needlessly ‘on guard’ all day long.