When an E-4 calls me "hey" or "hey man" knowing that I am an officer, should I bother to correct him?

I was told something as a young Marine and i took it with me when after serving 9 years as a Marine i went into the Army and it has always worked well . and that is ,In or out of uniform when you know the person to be an officer you address them accordingly . Sir or their rank No exceptions . Because it makes it to easy to slip up at the wrong time making both look bad . And if the officer never told you it was ok address them in such a casual way when not in uniform you don't period . And even if they have you respectfully decline and don't do it .

I think I greatly depends on the time and place and your relationship with that SPC. I had a great relationship with my officers, but if there was ever anyone else around I kept it professional. There’s a time and a place for everything.

You didn’t indicate if you were both in civvies when you saw him outside of work, but that might make a difference to him. A short conversation with him to let him know the expectation would probably do the trick since he seems to be addressing you appropriately on the job.

Custom and curtisies should all ways be observed. Regardless of rank on or off duty. to allow this it can and will cause problems at the job. Also as an officer you can get repriemanded if you get caught at home and that SPC is calling you by those names. AKA fraternization.

Lock their heals; do the on the spot
correction, and follow-up with the Company or PLT CoC. By following-up with the CoC not NCO support channel) it gives said SPC a second chance to have refresher training on customs and courtesies (C&C). You know how much1SGs having their Soldiers be placed on report by Officers. I can just hear
a Squad Leader, PLT SGT and 1SG each having a “friendly” conversation with said SPC. Picture him/her giving a C&C professional development class to every Fire Team in the Company in the course of a week.

So would you accept the SPC not obeying your orders? If so, why are you an officer. I realize that many in or society do not respect authority, but that is totally unacceptable in the military. Not only should this SPC be corrected, but his NCO chain of command should get involved and have this Soldier receive some extra training to further reinforce the need for respecting authority in the military. I had a Lieutenant once fail to recognize my authority, and that Lieutenant taught the next OPD class on the topic as extra training.

Here's the thing, regardless of the situation, the fact of the matter is you are an officer regardless as to how new you are to your rank a "hey" or "hey man" coming for an ENLISTED soldier (regardless of rank, but ESPECIALLY an E4) is very inappropriate. If you let it go, it shows them that you could care less and have no pride or respect for the uniform or military customs and courtesies. Which, you being an officer, I know this is NOT the case because of the hard work and time and effort you put in to become a military officer. That in and of itself takes a good amount of pride and respect. Use that pride and respect and professionalism, that I know you, as an officer, have and call the E4 out. Let him know that while you respect his rank he should be respecting yours as well. You worked hard for your rank, a "hey man" in inappropriate in the AO. "If you can't remember my name or are not able to identify my rank, a simple Good morning/afternoon/evening, Sir, will be suffice" Continued actions of this nature could result in non judicial punishment IAW with UCMJ article 92 failure to obey a lawful order (albeit verbal, written or general, not abiding by by military customs and courtesy is a direct violation of the UCMJ) Let him know you mean business and this behavior will not be tolerated. Plain and simple.
Good luck, Sir hope this gets resolution for you quickly.

I have a question, is this happening more often today than in the past?

Yes, you should this is unacceptable decorum. When this Spc gets his education and time in service and decides to get a commission he'll be afforded the same right.

As former AD Enlisted Soldier and a Reservist now, I can honestly say Sir that you should definitely correct him. In my MOS , we worked with our Officers on a daily bases. Sometimes as a unit we would go out together for meals,etc. I always addressed them as Sir or Ma'am even if I was in civilian clothes. I did it to show respect, but also because that was what I was taught.