Replace "serial killer" with "stranger" and you have a very good reply.
If they continue, remind them it is part of the customs in your area (aka western civilization) to introduce yourself first, before starting a conversation with a stranger. That way, you can be acquainted, and not be strangers anymore.
People are disarmed by this. The moment they become less anonymous, they become more human, and therefore reasonable.
Etiquette did not arise from nowhere. It specifically addresses societal problems like the one being discussed here. Remind people about their responsibility to be polite and civilized.
Replace "serial killer" with "stranger" and you have a very good reply.
If they continue, remind them it is part of the customs in your area (aka western civilization) to introduce yourself first, before starting a conversation with a stranger. That way, you can be acquainted, and not be strangers anymore.
People are disarmed by this. The moment they become less anonymous, they become more human, and therefore reasonable.
Etiquette did not arise from nowhere. It specifically addresses societal problems like the one being discussed here. Remind people about their responsibility to be polite and civilized.