> A blunt response like, "Fuck off. Don't talk to my son.", followed by walking away from her, may have been harsher and not particularly polite, but perhaps it'd cause a person like her to avoid such meddling in the future.

No, it would solidify that persons' belief that the people were bad people and embolden her to act more swiftly next time.

Confrontation and escalation with swearing doesn't teach people a lesson. It makes them dig their heels in.