As society evolves, habits that have felt polite or normal to one generation can become rude or dismissive to another generation.
Comparisons

While older generations may say phrases like “back in my day” to pass on earned wisdom or simply paint a frame of reference, younger generations hear a lesson they didn’t ask for.
What they really hear is, “You don’t have it as hard as I did.”
But in reality, younger generations are faced with record-high living expenses, astronomical student loan debt, and huge career instability. They don’t need someone telling them how easy they have it.
Phone calls

To older people, picking up the phone and dialing a friend or loved one was the most common and reliable form of communication. It was seen as polite, proactive, and thoughtful to randomly call someone.
Millennials and Gen Zs grew up with instant communication at their fingertips. A random, ringing phone can feel like demanding someone drop everything they’re doing to give you undivided attention with no warning.
Texting periods

To the earliest generations of digital messengers, ending a sentence with a period was the proper, polite way to write.
However, younger people who have grown up with communicating solely through texts, tweets, and chat messages tend to view a period at the end of a sentence as aggressive or cold.
That lonely period at the end of a phrase can make you feel like the sender is mad at you, ending the conversation, or generally unhappy with your message.
Public loudness

Some Boomers tend to speak loudly on their phone on the street or use the speaker function on the train or elevator.
Speaking loudly on your tech devices in public spaces is frowned upon by Millennials and Gen Z because they value digital privacy and etiquette. Everyone around you values silence on public transit like a communal courtesy.
Giving advice

For older generations, dishing out advice is one of the ways they care for and show interest in a younger person’s life.
Younger generations already feel managed by society. Unsolicited advice can come off as condescending and imply that you think they’re too stupid to figure things out.
Reply all

“Reply all” to send a quick thank you or acknowledgement was considered good netiquette by workplace professionals who entered business before the email overload began.
However, younger employees who are already overwhelmed by emails each day see another notification as an actual interruption to their workflow. What’s harmless to one person can make someone who sits at a desk all day feel like they’ll never catch up on their tasks.
Misplaced quotes

Putting quotes around a word to give it emphasis (writing “Sale!” on the sign at your garden store) used to be an acceptable, normal practice. Now, almost any use of quotation marks can be interpreted as sarcastic.
If a millennial or Gen Z sees a word with quotes around it, they believe you’re saying the opposite of what you really mean. This causes confusion and can come across as passive aggressive.
Drop-in visits

Showing up at someone’s door without a scheduled time was normal etiquette back then.
However, younger generations view their homes as their safe space. Someone literally knocking on their door can cause anxiety. They like to know when to expect guests so they can mentally prepare for company.
Career questions

“How long have you worked there?” “Is that a real job?” These are microaggressions older people say to younger people who have jobs that weren’t around when they were in the workforce.
They may be just trying to understand more about the job. However, to the person who has that job, it feels like the older generation is criticizing them or questioning the validity of their work.
Softening phrases

Older people say “No offense, but…” before they say something negative to try to soften the blow.
This was traditionally taught as a way to soften criticism. To younger people, it serves as a warning, literally telling them an insult is coming.
Over-explaining

Parents, teachers, and older bosses often go into painstaking detail about how they want a task completed.
Millennials and Gen Z learn most via self-teach YouTube tutorials. They feel smothered by older generations who think withholding knowledge from the younger generation is some sort of crime.
Inflexible work times

For many older generations, schedules are rigid. Lunch is from noon to 1PM, meetings will always start and end at the same time.
Millennials and Gen Z thrive on flex schedules, working from home, and caring about the work they put in instead of the hours at their desk. For them, these set times are archaic and hurt productivity.
Digital resistance

Sometimes older people will refuse to adapt to new technology, like digital kiosks or mobile apps, as a way to resist change.
Younger generations are frustrated when older people make them (whether their family members, coworkers, or waitstaff) do their digital labor for them.
Sources: Please see here for a complete listing of all sources that were consulted in the preparation of this article.