I can see why parents might want to watch their language. I told my grandfather to fuck off when I was 2, because I overheard my dad saying it once. Grandma thought it was funny. Grandpa, not so much! :lol:
My dad made sure to use other words after that.
However, I think it's ridiculous that the lady called the cops. This is when you make it a point to your children that this is NOT okay, and turn it into a lesson. No need to bring other people into it.