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

As the officer, you're assumed to be the leader. Lead by example and you will gain some respect. Get the counsel of your NCOs first and you will gain their respect. Make corrections where you have to to maintain correct standards, and make sure the SPC's chain of command is kept in the loop. The chain of command will respect you as long as they're informed.

I'm not saying you have to act on NCO counsel, but good officers always improve when they at least listen.

Where were you? Were you in uniform? How do you know this person? Command has always taught us to consider all the facts before issuing a command.

ABSOLUTELY!

I’m a recruiter and I don’t allow my civilian DEP members to call me that.

CPT (Join to see) Sir, it appears that this SPC needs a little light correction. I state light because he may not realize it is inappropriate to address an officer whether on-duty or off-duty by anything other than sir. Others have mentioned it in their response, but I will add it again, there is no such thing as being "off-duty". When you raise your hand, repeat the oath, and sign on the line, you are a Solder 24/7. One thing I am consistently "seeing" and reading about on different military type websites is how military professionalism has become almost extinct. This could be from various reasons, but allowing this type of behavior to continue will only exacerbate the issue and could lead to problems for him, and you, down the road. Look at it this way, he is transferred to your unit and you are the unit commander, and he is standing in front of your desk pending non-judicial punishment for an infraction, how would you handle it - professionally I would assume. This situation is no different. Likewise, the scenario I provided could very well happen. The "casual" attitude will lead to an awkward situation during that type of scenario. He may think because you both seem to be on "casual" terms, his punishment for the infraction will be that you will only apply a company grade Art 15 with everything suspended, or maybe just a letter of reprimand. Just a couple of things for you to ponder while you decide your best course of action for this situation. Notice that although I have been retired since early 2008, I still called you sir.

%100 What SFC O’Mally said. If you let it “slide” you’re saying that’s ok when it’s not and you have too become part of the issue.

If he knew you were an officer, then he was disrespectful and You are responsible for correcting the situation. If you can not do that, you should resign. I was enlisted to E7 and commissioned to O5.

If still on active duty, correct him. If not. respond , "Yo". As a lieutenant, don't get too puffy.

You would not be in the wrong to, "Check that azz immediately!" It irks me to the bone when subordinates disrespect rank or ranking staff member! If you teach him/her immediately/ correctly, there is no, I didn't know, if it ever happens again. Whooah!!

Short answer, yes you should. The SPC probably thinks because it’s off duty it’s ok. Nothing wrong with correcting the issue so he doesn’t do it to someone who will blow it out of proportion. Never pass up a “teachable moment”.