Similar to the E-2 question, how would you react to a young 2LT who is being unprofessional with a strong sense of entitlement?

I wouldn't say anything to him, I have better things to do than waste my time correcting a 2LT for nonprofessional behavior. This situation is for soldiers and sailors who have nothing to do, or that need to get a life. When I was in I had a job to do, which didn't include going around looking for un-important corrections.

I was only an HM2 so I usually kept my mouth shut when out and about. Unless conduct impacted the mission or medical well-being of my Marines of course. However, I don't recall seeing major levels of fucked-up ness with Marine officers. Junior Navy officers could be complete screw-ups and were snotty. I often still would mind my own business unless it impacted my work or a patient. Jr nurses could be bossy and nasty or very high-strung around Corpsmen until they got things figured out. I never held it against them.

As an NCO your best bet is to find out his unit's first sergeant and bring it to his concerns and let the first sergeant handle the incident through his chain

In todays world I would get him in a video on my phone and send it to his commanding officer. Done

I would follow that 2nd Lt until I find their command or we walk off the face of the planet. You better believe that I would happily offer him up as tribute to his CO and 1st Sgt. If they don't care, I'll stop by Battalion.

To be perfectly honest as an NCO, for something like an officer shopping with a headset on I probably wouldn't have said anything to begin with. It's not a battle that would be worth my time. I would hope that another officer would observe and make the correction. If I did bring the deficiency to his attention, and received a rude response, I would have politely asked him for his name, and command and would have followed up with the next person higher up his chain of command. I would also take down the names of anyone who may have witnessed what transpired.

Send him to psychiatry to evaluate for Narcissistic Personality Disorder which will hopefully get him out of the military early. If I was young again, I would never trust my life to one of them.

Someone told me many years ago,that there was no difference between a 2LT and a private.As I whent thru my career of almost 30 years,l got convinced that was true.

Attitude adjustments need not be obvious. The lieutenant would either correct the current evidence of his ignorance or we would be riding to his unit office. Strong letter to follow.

As a senior SNCO, I would respectfully speak to the LT. IF a gentle and respectful conversation did not correct his attitude, my next step would be to talk to the CO. with him in tow!
I have had to do this once in 20 years! Never met a grunt 2ndLt. Who thought he was a waterwalker, but have met a few support Lts who tried to be very hard to work with. So, if a respectful conversation failed, Mister DS, had a talk with the CO. Never heardrum what the CO. had to say, but attitude was gone from then on!