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 would let it go. If he continues this behavior in public it’s only a matter of time before a senior officer sees this and puts him in his place. You did your job and respectfully pointed out the deficiency.

Its one of things you have to get past. Back in the day, we didn't talk to Officers....Salute and move on. When I left service after 35 years in 2011. LT's seem to be very agressive, self serving and don't have much leadership skills. True leaders get things done by providing direction, resources and followup. Now its get it done....Bye....Those leaders I call Sea Gulls, they do a whole lot of yelling and screaming and steal all your french fries, then in a blink of an eye there gone. They don't provide as above, task, conditions or standards. I think Enlisted in general are absolutely more challenged than years past. The equipment is very technical. The most advanced items in my ground pounding days was a Compass, a simple radio, A1 Rifle, and Rope. Being new as a LT is a stressful time. Screw up's are easy but some get you out. I am not supporting crazy LT's, but I have to follow them to the grave. I may not like them, but there is an Oath. LT's don't have to follow Enlisted. If the LT is smart they will listen but the buck stops with them.

Ask the Lt what unit he is from and approach their command and explain to his or hers CO and 1SG. See how quick the LT's attitude is changed. Chain of Command also includes theirs too. If you cannot get the correct response from the LT, then you follow up with their Chain of Command. No unit wants to feel that their leaders are unapproachable and entitled. You don't want to get into a shouting match. If there is a senior officer around at the moment get their attention and address the issue.

I would pull him/her aside and have a private discussion about their conduct.

If the Lt. Ignored me, I would address there conduct and their reaction to my corrective action.

Most commanding officers listen to SNCOs, and have their back with dealing with Jr. Officers.

It doesn't matter if it's the Chief of Staff. If something is wrong you have every legit reason to correct them. Just be tactful.

So there I was! It was probably 2017 I'm doing Physical Training, as I'm running down the road on post I see a CPT playing music (using his phone). I can't quote a reg or current policy, but I know at that time you were not allowed to even have your cell phone during Physical Training (III CORPS policy). So I run up beside the CPT is obviouse he's new on post, so I explained the policy. The CPT uses the excuse we are a loud to use head phones etc in the gym etc where I came from etc etc. I restated the policy and just so happened about the same time I'm reiterating the policy my Division Commander happened to be running by so I said I don't make the policy I simply enforce them; however, you could always refer any questions to BG (name left out on purpose) who just so happens to be that man right there. And I just went about my business. Bottom line I made the correction I can't punish the CPT (obviously enlisted have no true authority over an officer) but I did my job.

Respect his rank, should that person have a higher rank, give that person the respect they're entitled to, then write his or her name down and had it over to your Command, see where it goes, you did your best to bring up the discrepancy, sooner or later a 1st LT, CPT, or a spouse of a Commander will address it to that person or a Retired, so someone will get his or her attention and it wont be Good

Politely remind them of policy and bid them a great day! If the 2LT is in my unit, I will refer the matter to an officer in their chain of command regarding the matter and keep smiling

I wouldn't say a word... If the dumb ass wants to look unprofessional then let him.

Ask the 2LT who his commander is. Also get all his information that you can; full name, unit, PLTN SGT, Fort/military base he is stationed at. If he will not provide any of this information at least get his last name. Remember to write down the time and date of the event, where the event happened and exactly what was said, might also get a picture of him with his headset on with your cell phone. Once the 2TL is finished and he goes to his car copy down his license plate. You can then find out all the info you need to properly report this young officer to his Commander from the MP's.
As a LTC I am sorry you had to go thru this. This 2LT has failed in military bearing and other areas of professional conduct. It is apparent this officer needs to familiarize himself with AR-670-1