Time was, you'd use this term when you didn't know the name of the letter recipient.
But "in today's world," Pachter said, "that can get you in trouble." If your kid is applying for an internship, for example, make sure they use a "non-gender-specific, non-sexist term" such as "Dear Hiring Manager."
Instead: Business Insider previously spoke with Amanda Augustine, career advice expert for TopResume, on this topic, and she recommended searching on LinkedIn to find the name of the company recruiter or hiring manager who originally posted the job.
Simply writing "Dear Sir" or "Dear Madam" makes you look like you haven't done your homework.
Exchanging calling cards
The etiquette territory "that changes the most quickly tends to be the manners around communication," Senning said.
For example, if you take a look at a 1920s edition of an etiquette handbook, there could be a whole section devoted to exchanging calling cards.
These days, Senning said, calling cards are largely obsolete — and many parents are instead concerned with how their kids are interacting with other kids on social media.
Both Pachter and Senning said this is tricky territory, too. Only a few decades ago, you'd always have your kids call your friends Mr. and Mrs. Smith. Today, some of your friends might prefer it that way, while others might prefer Bob and Deb.
"It gets a little confusing," Pachter said.
Instead: If your kid isn't sure how they should address another adult, Pachter's advice for them is to err on the side of formality. "You can always be a little more formal and work your way down," she said, "but it's a lot harder to work your way back up."
Letting a man pay bills, carry packages, pull out chairs, and open doors
Here's a tricky area that Pachter pointed out.
For example, maybe at home, Dad does carry the grocery bags for Mom. That doesn't mean that at work or school, your son should insist on carrying a woman's bags — she might consider it insulting or awkward.
Instead: Pachter's general rule that she recommends teaching kids is "help anybody who needs help" — regardless of gender.