we switch on our imagination and generate in our mind terrible pictures, thinking that "it would be better to say this way", "his look was so strange", etc. These are needless pictures. Doing this way, we add negative emotions. That's why after an unpleasant conversation you should switch off your intellect and in no circumstances think out new details.

And the last, but not the least! Don't keep negative emotion inside! If we oppress our emotions, we push them in the depth of ourselves. Later, they become apparent at unsuitable moments. Thus, you should be able to throw away negative emotions. Not on other people (your parents or friends), but on "neutral territory". For instance, if you are alone at home, you may shout, sob or make physical exercises.

Hope these ideas would be helpful for you not to become infected with negative emotions, or if any, be able to throw them away! Good luck!