” Problem if the teacher is a secular Jew (helps to be familiar with the civil rights laws on the matter).”
Akuperma, explanation?
“And if you are explaining Hol ha-Moed to a frum Jew who ignores it, best to have the Shulhan Arukh with you.”
If they won’t listen to you, halachically it might be better not to say anything unless they asked. If they asked you, it’s probably different.