It's definitely one way of doing it.
I don't know that it's possible to NOT offend some believers.

There is no wrong or right here.
But you might want to keep in mind that no matter how differing opinions are presented, there will always be some who will CHOOSE to be offended, and get all bent out of shape. Oh well ...

I don't feel I'm offending my religious friends when I say I don't believe in Supernatural Deities. That usually makes them think.

I prefer to keep my spirituality within the natural world. Is there something out there we don't know about? Maybe.

But until then, let's just work with what we have, the wisdom of humanity through the centuries, personal and collective histories and experiences, social support networks and civic laws. Not sure why we need a book stuck in an age we can no longer identify with.

If your friends are truly offended that you don't believe in their religion and you are not doing anything to provoke them like taunting their beliefs, then they are not your friends. If you accept them for who they are, then they should accept you for who you are.

Why would your religious friends BE your friends if they would be offended by your beliefs?

If you want to be accurate, tell them you hold no gods.

If you want to be inoffensive, tell them religion is personal. You may choose to mention, or choose to omit, that lack of religion is also personal.

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It is impossible to avoid offending some people. I don't believe in ghosts either.

No, you are not wrong. The onus of proof is on the irrational believer, not the rational skeptic.

I say something Linus Pauling once said. I believe that all complicated phenomena can be explained using simpler scientific principles.

If your worried about offending them, then you're wrong. They believe you will go to hell and be tortured for eternity because you don't believe the same things they do. How can you be more offensive than that to them?

If your ready to take a stand against superstitious ignorance, then, no, your not wrong. The door swings both ways.

If anyone does not have reproduceable evidence then it is possible they are wrong. The burden on them, not you, is to produce the evidence. Why worry?

Offense is taken not given, it is not your problem if they choose to be foolish.

Yes! Show me yours & I'll show you mine!

Your statement is right, but if you don't want to offend your friend maybe " I respect your right to have a faith, but I do not share your religious beliefs" might be better...

Tell them you have a friend who has experienced ghosts and has seen a UFO. Now I know what is coming next so I will tell you that I thought the UFO was a helicopter, I was told by a person in the FAA that it was a UFO and he showed me how he knew. The ghost story is true and I cannot explain it. I know Science and the scientific method. What I experienced made no sense to me at the time and I thought the ghost thing was fake until I was having a conversation with several other Doctors about the incident. They knew the circumstances, believed me an said they were glad the experience did not happen to them. I will answer any questions to the best of my ability.

Any words you use to describe your beliefs, or lack thereof, is just fine.

There are lots of ways to make the point, and I use different ones depending on context and audience. That being said, I really like your ghostly approach, and look forward to taking it out for a spin ...

Welcome to the site, your comeback sounds fine to me.
But make sure you possess The holy hand grenade of Antioch, just in case.

Mention Santa Claus & the Easter Bunny. Then swing into Pastafarian Theory.
Seriously, why aren't you changing the subject and if they persist, telling them to knock it off?!?!

[sarcasm] When talking about supernatural beliefs with you friends, always make sure that it is apparent that you are attacking them and not their beliefs. Do this by explicitly saying it up front. Never let them have a word in edge wise, and most importantly, do not listen to them and what they have to say. Under no circumstance should you let them have any ground or be allowed to feel like you could possibly be wrong. Confidence is key, don't show any signs of fear or weakness. [end/sarcasm]

Alternatively, do something like this.

Yes... And there are about a dozen recent threads on how to do it.

I am Ignostic as it better describes my position than simple atheism, so I use that and have for years now.

A side effect of it is that few believers have ever heard the term so it does not carry the baggage that atheist does.

I am an Ignostic

I was raised a believer
AS a believer I thought understanding God of the utmost import.
SO I studied that.
Which is why I am today an Igtheist/Ignostic

Ignosticism is an Epistomologic position; it is a set of ideas refuting the importance of determining the existence of God. It claims that knowledge regarding the reality of God is altogether unprofitable.

It is the idea that every theological position assumes too much about the concept of God and other theological concepts; including (but not limited to) concepts of faith, spirituality, heaven, hell, afterlife, damnation, salvation, sin and the soul.

Ignosticism or igtheism is the idea that the question of the existence of God is meaningless because the term god has no coherent and unambiguous definition.

IF you cannot even define what you are talking about, or consider it beyond human understanding, how is it you can claim to know anything about it and keep your intellectual integrity intact?

It helps to better know your audience. I mean, if you are dealing with Harry Potter worshippers it might make a difference than if you are talking to Scooby Doo style ghost believers.

Not wrong leave it at that