There is one type of behavior towards a person that is universally disliked, and that is to disrespect someone. Some people just cannot handle being disrespected, as a disrespectful person will also tend to be condescending. They are putting the other person down to make themselves feel better. In public situations, there are some loud and obnoxious individuals who may randomly talk trash.
When you talk trash about someone loud enough that they overhear, you should expect to receive consequences for your words. Of course, those with the personality to trash talk strangers in public in the first place are likely to think they are in the right in any case.