How would you react if you were on a flight where a family was boo'd for being allowed off the plane first to receive their soldier's body?

I would be honored to be part of a brothers homecoming. I would salute him and his family.,

First of all, my deepest heart-felt condolences go out to the service member’s Family, his/ her military team, friends and you, for your loss! Thank you for your service and sacrifice! Families Sacrifice, too!
As difficult AND as painful and repulsive as your narrative is, we cannot engage with-ignorant people … it really isn’t the Way-of-the Warrior we just lost. Ignore the ignorant!
Fortunately, you can control YOU and your actions alone! Keep your Military Bearings intact; although, it is not easy. Remain professional, this way you show your strength, intellect, and maturity. That is the Warrior’s Way! This way you bring Honor to Yourself and our fallen heroes! RIP

We live in a time when so many think they are much better than everyone else. Many lack respect or empathy the elderly, disabled, or in this case the grieving family of a soldier. The missing ingredient of kindness, and being treating others as you want to be treated, is no longer even considered. The "GOLDEN RULE" has been lost lost and no longer taught. For some of us who are in our seventies we remember a time when it was not this way. Our future does not look as bright as it once did.

No point in lecturing the uneducated mass, but personally I would be extremely angry and ashamed at the disrespect being shown.

Some people simply have no class. We went to the airport when my brother's body was flown home. There were countless flight delays and issues that made the flight arrive late. The airline actually made special arrangements to have another plane meet his plane at their previous stop, as that first plane had a mechanical issue. Otherwise, we were told that the passengers would have been put up in hotels overnight. They only made these changes because they were bringing a Marine home. Our family was staging in baggage claim, waiting to be escorted onto the field. The passengers had already arrived there also. They made a brief announcement, that bags would be delayed while a Gold Star family received the body of their Marine, who had been on their flight. Most had no issue with this. Two assholes decided to comment that they'd waited long enough already, and this was bullshit. One of my other brothers and I heard this, and were not exactly happy. Fortunately, one of the Marines from the family detail also heard them. He immediately proceeded to explain that the only reason they had gotten this far, and weren't stuck in some shitbag hotel somewhere was due to the Marine in the belly of the plane. He then offered that if they had further comments to make, he'd be happy to escorted them outside to discuss their complaints with his family. They declined.

It would be very hard to maintain my military bearing in that situation.

Asked the flight crew to announce "Ladies and gentlemen please pause for a minute and help us honor a family who have lost a love one giving who has made the ultimate sacrifice in protecting the right we all continue to enjoy to this day." Thank you!

I do not believe this has ever happened. I have heard of it once before in TEXAS, and i called bullshit then too.

However to answer the question:

You keep you military bearing and stay quiet, especially if you are in uniform.

If you are retired or otherwise no longer serving just shut the hell up too.

Two wrong don't make a right.

The measure of a patriot is not how much he agrees with you; The measure of a patriot is how well one can control oneself, when faced with someone one disagrees with.

I would go Marine all over his ass.

If I was on that Patriotic detail, I would sternly address the miscreant in matter of fact terms, and if that didn't correct his attitude, I would personally adjust it.