What is the BEST example you've seen of the millennial mentality in the military?

Joining the military during a time of war.

Same answer ...kind of
This forum is packed with examples... from the awesome attitude to earning a promotion, job, schooling vice some snotty "I'm entitled"

TO standing up to what's right because the service is requiring the INDIVIDUAL to become a team player, and they recognize that is what wins ....the team, not the individual, though the individual must be strong, mentally, morally , physically, and have an individual desire to never quit.

Dozens of driven, capable and devoted men and women striving to be the best they can at their tasks. Working to accomplish their given missions, take care of their Soldiers, Sailors, Airmen and Marines (and sometimes even civilians) and maybe help some other folks better at the same time. And best of all, intent on developing those around them to higher levels of achievement and leadership.

SGM Matthew Quick Wow... crickets.. No really, Met some really sharp soldiers OCONUS as a contractor.

Honestly, I wasn't sure what exactly you were looking for in your question. The "best" example of the millenial mentality is actually pretty negative, but it looks like you're looking for a positive response so I'll share both.

The "best" example of the millenial generation is when I corrected a junior Marine for a single piece of work that had 9 errors on it and they wanted to argue that it should only count as one error because it's one piece of work. My response "Listen Marine. When a jet falls out of the sky, no one is going to care if you made 1 error or 9 errors. There is no partial credit when a pilot's life is in our hands". I was livid that someone was actually going to argue semantics over how I evaluated the quality of my Marines work because they didn't want to look like they made mistakes. That's what I'm calling my "best" example.

My most positive example came from a Marine I raised from a junior all the way to an NCO. A little slow on the uptake, but always asking questions. Always trying to learn. Always trying to be a better Marine. He reminds me of myself sometimes. Always putting forth the best effort.