This question was inspired by the comments (now deleted) under another question.
My sister in Williamsburg Brooklyn noticed that Orthodox male strangers were glaring at her for unknown reasons while she was on the subway or the bus. It is now clear that they had a problem with her singing to her small children on the subway. Her son has special needs, he is largely nonverbal, and he sometimes has seizures. When she sings to her children, her only intention is to soothe them (especially in the event of a seizure) and keep them calm and quiet. As a mother traveling on NYC public transportation alone with her children sometimes at night, she was intimidated and felt a bit threatened by these men glaring at her.
Obviously, everyone is entitled to feel however they want to feel, and these men are free to believe whatever they wish. But it is possible to feel something without causing distress to another person. It is possible to keep your feelings to yourself, or to share your feelings with likeminded individuals. I am wondering if Jewis custom, practice, law, etc, has anything to say on this issue:
Someone who may or may not be Jewish is doing something that would generally (in the broader society) be considered inoffensive in a public place, but is or may be a violation of Jewish law. Most people in the broader society, including the person doing the activity, don't know of the law in question and think the activity is normal. An Orthodox person in the same area believes that this activity is problematic.
Is there justification for the Jewish person to cause discomfort or distress to strangers in response to an unintentional and inadvertent offense? What sources are applicable to this issue?
Note: This question is not about kol isha; it is about the response.