We all know free speech is not an absolute; Justice Oliver Wendell Holmes’ argument about “falsely shouting fire in a theatre” is Exhibit A. There are also things you cannot say on a plane; doing so may not land you in front of the Supreme Court but it could get you kicked off your flight. A few examples.

1. “Did you pack the bomb?”

There are millions of variations of this joke, but none of them are funny, not in airports and not on planes. The TSA has had to pull many such comedians out of security lines and occasionally arrest them; it happened to an NFL player last year.

2. “Are you crazy, no one tips a flight attendant!”

Not so fast. Frontier Airlines has allowed tipping on the food and beverage sales by flight attendants for the past three years -- tips that were then pooled with the rest of the crew. What’s new is that, since January, individual flight attendants get to keep the tips they personally bring in. Of course, you are under no obligation to tip, but it is a thing on Frontier. The question now is, will other airlines join in? Hard to say but remember, tipping used to be unheard of on Uber, too.

3. “I don’t want to buckle up at this moment.”

When the pilot gets on the intercom and tells you to do something, like take your seats or buckle up, it is not a suggestion. As the Federal Aviation Administration puts it, the pilot is the “final authority as to the operation of that aircraft” and you are obligated to obey. You have to listen to other crew members, too. After all, when they say buckle up, it often means turbulence is on the way.

4. “I can have that seat because no one else is using it.”

In days of yore – well before 9/11 – after planes took off, folks in coach could often spread out, sometimes to better empty seats. Today, empties are rare, but when they do exist, they may be in premium economy, which comes with a higher price tag.

5. “I’ll just hang out with you for a while.”

That comment is directed at flight attendants working in the plane’s galley, which is a small and crowded spot at the best of times, and not meant for passengers. This is where flight attendants work; you wouldn’t barge into someone’s office uninvited, would you?

6. “’Nother beer pleesh.”

Watch what you drink, because things often end badly for intoxicated passengers. Like the young man who went on a drunken tirade during a transatlantic flight last year; he has just been sentenced to six months in jail.

7. “Do you know who I am?”

This one I can’t vouch for, but it’s so good I have to share: Supposedly a harried gate agent for Southwest Airlines was dealing with several passengers because of a cancelled flight a few years ago when one of them cut in line. The agent said nope, go back, whereupon the passenger yelled, “Do you know who I am?!” The the agent then calmly picked up the mic for the public address system and said, "We have a passenger here at the gate WHO DOES NOT KNOW WHO HE IS. If anyone can help him find his identity, please come to the gate."

Finally, whenever and wherever you travel, I hope you always get a good deal on your plane tickets, and that all your flights go smoothly.