For any sailors or marines here, how do you informally address a U.S. Navy petty officer? Do you just use his or her name? Or is there some informal title? Thanks.

Depends, do you know/like/work with daily the individual. then your probably going to simply use the persons last name, or nick name if they have one. If your an Non-PO. (E1,2,3) then formal address is simply "Petty Officer Lastname", and you should almost never be using informal names for ANY Petty Officer, let alone senior enlisted, etc. If you start breaking it down into Petty Officer First Class, Second Class, or Third Class, then your just being a douche. Sometimes the specific rank third, second , or first is ok or needed. Like if you were answering a specific query form an officer or a very angry senior chief.. " I.E. "Sir, my direct supervisor is Petty Officer First Class Johnson".. But other than that 90% of the time just "Petty Officer". Its kind of like Sergent for the army or air force your generally ok calling most mid level enlisted Sergent, even if it isn't their official title.

For a specific answer to your question Informal address in Navy and all the Military would most likely be just the last name.

Clear as mud right?

I had to read it more than once, but after that it made sense. I suppose it's just that you have to be in the military to understand the military. That was the information I was looking for though, so thank's for answering.

Yes he is correct under most conditions...

Now when your 1st Class Leading Petty Officer(LPO) picks your 6' 4' 235 pounds off the deck, with his left arm, and draws the right arm back...then points his right index finger at your face and states "Petty Officer "Blank" do not ever address me again like that." and I responded "Aye Aye Gunner's Mate First Class Petty Officer Ahnee."

Rule 1 do not mess with Hawaiians or other Polynesians.

I'm not sure of the US Navy but in the Canadian Navy we refer to Petty Officers as P.O.s while Chief Petty Officers are just Sir/Mam.

Well while I served, calling a Chief Petty Officer, Sir or Mam, was a quick way to get on a CPO's bad side. Nice reply was "I work for a Living...."

That response always drove me up a wall. The only thing worse then a petty stupid military tradition is a petty stupid military tradition propagated by HOLLYWOOD.

I am reminded of the short time I spent in the U.S. navy. Three days after arriving in San Diego, A fellow recruit, while being screamed at, panicked and replied " Aye-Aye, C3PO!!"

From that experience I learned that ranking naval personnel reeeallly don't like being called translator droids.

What would an officer say, though? "Chief"?

Officers call Chiefs Chief, unless they're a Senior Chief or Master Chief. Heaven help the junior officer who fucks up that distinction with a person who may have, literally, served longer than they have been alive.

I just got out of the Navy six months ago but I think I can help you out here.
So a little background that will help. US enlisted ranks run from E-1 to E-9, these ranks can be grouped into triplets of relative authority. E-1 through E-3 are "junior enlisted" and by default are referred to as Seaman (It's more complicated than that but calling a junior guy Seamen Shitforbrains is almost never wrong, you've either promoted them a couple times or pegged their current rank). E-4 through E-6 are Petty Officers although the difference between each rank is significant (I'll get to that later). E-7 through E-9 are ALWAYS referred to by their complete rank, except for E-8's who often go by simply "Senior" (E-7=Chief, E-8=Senior Chief/Senior, E-9=Master Chief/Your Master/Mistress After God). Jesus that's really complicated when you write it down... anyways.
The other thing to keep in mind is that the Navy has to be different from everyone. It's a point of pride that we do things our own special Navy way hooyah? Because of this, naming conventions are complicated by one further axis of madness: Rates. A rate is a persons job, it's what they're trained to do and, unlike every other service, the rank patch that they wear on their dress uniform reflects this. I was a Hospital Corpsman so my "rate" would be referred to as a HM. I had some buddies who were Hull Technicians (they weld shit and... uh... deal with shit... it sounds better at the recruiters office) so their rate would be a HT. There are something like 60 odd rates in the Navy and they keep merging and changing their names. Despite this, rates are important to Navy folk. Most people have at least a little pride in their rate. It means you have special training, knowledge that other people don't have and probably most importantly a long and proud history. I am proud to have been called a Corpsman, it was a special thing for me to know that I had taken up a job held by many more worthy men and women over the years. er... but that's getting off topic. What I'm trying to say is that generally speaking people will want you to acknowledge their rate whenever possible. It's also easier to say HM2 Oorah rather than Hospital Corpsman Second Class Oorah (Point of order, OORAH!!! *Blood curdling scream* is a Marine Corps thing but Corpsman generally get to steal it).

SUPER SUMMARY(Examples are in order of formality with a Hospital Corpsman/HM used whenever appropriate)!
E-1/E-3 Referring to each other: Yo dude.
E-1/E-3 Referring to a superior: Petty Officer LastName, HM3/HM2/HM1 LastName, HM3/HM2/HM1
(RP Note: With rare exception, E-3 and below rarely get into rank based dick waving contests. You get promoted from E-1 through E-3 by not getting in trouble so it's not really an accomplishment to BE an E-3. In theory an E-3 should be able to boss an E-2 but in reality it comes down to what the E-4, or E-5 above you thinks. If your immediate supervisor thinks the E-2 has their shit together, they may in fact put them in charge with a bunch of E-3's. In other words, Yo dude will suffice as listed above)

E-4/E-6 Referring to a subordinate: Seamen, Fireman(FN), Hospitalman(HN), etc a lot of rates have their own special E-3 and below name) Recruit(E-1)/Apprentice(E-2)LastName, You!!! YES YOU! STOP FUCKING AROUND WITH THAT AND FUCK AROUND WITH... THAT... OVER THERE! NO THE OTHER ONE! FOR FUCK SAKE?! DON'T THEY FUCKING TEACH YOU ANYTHING IN BOOTCAMP ANYMORE? *Anguished Scream of Frustration*
E-4/E-6 Referring to each other: Petty Officer LastName (This is formal and technically correct but an E-4 referring to their boss, an E-6, in such a way will probably get an earful. People like to hear their rank), HM3/HM2/HM1, Yo dude (You can generally call a guy one rank above you, but within your triplet, by his last name or whatever. It's not strictly proper but as long as it happens out of the public eye it's not a huge party foul)
E-4/E-6 Referring to a superior: HM2/1, Chief, Senior Chief, Senior, Master Chief, Sir/Ma'am, Midshipman, Ensign (O-1), Lieutenant (O-2/O-3), Commander... etc But officers are usually pretty anal about their rank (especially if they're a Commander or better OR prior enlisted). For RP flavor I would point out that the Enlisted Section has long ago mastered different ways of saying Sir so that it is either a mark of respect, fear, or disgust/disdain.
(It should be noted here that E-6 are generally the Boss of a department. HM1 Hardass is the guy who you're going to see every morning at quarters and who is going to hand out work assignments and so forth. Calling HM1 by the proper rank is kinda important)

E-7/E-9 Referring to a subordinate: HR/HA/HN/HM3/HM2/HM1/Chief/Senior Chief/Master Chief, Chief, Senior. YOU, Hey You, Monkey, Asshole, Shithead, etc. Usually combined with a command.
E-7/E-9 Referring to each other (But only to an equivalent rank, never above and below): Chief, Yo dude. (Chiefs tend to have a hard-on for formality, it's part of their job description. As a result they tend to refer to each other by rank unless they're behind closed doors or out for brews. I've heard Chief used informally between different ranks of Chief but I'm not sure if that's common practice)
E-7/E-9 Referring to Superiors: Chief/Senior Chief/Senior/Master Chief, Sir/Ma'am, <Appropriate Rank> and IN SOME PLACES WHEN REFERRING TO THE CAPTAIN OF THEIR SHIP: Skipper (I've seen this happen like, twice and they were both in informal situations with captains who were "chill')
(Fun fact! Chiefs are actually charged with training junior officers. A Chief has at least 8-10 years under their belt and as such knows this game a little better than some Journalism major who couldn't find a job and failed upwards into leading the Supply Department. Chiefs can therefore correct an officer, politely (in theory) and in private (in theory and in practice... usually). Good senior officers (Commanders, Captains) generally support Chiefs for verbally working a junior officer over for being a dribbling idiot. As with all Naval traditions, shit varies by command and situation)

And now you know why the Navy feels it's important to devote an inordinate amount of time to "Naval Customs and Traditions"... just so people will know how to refer to each other.