If I said that I'm an atheist in your nation?

[Vaniri]

Meh live and let live.

[The Federal Kingdom Of Zuhi]

Zuhi's government honors all Religious beliefs, even citizens who do not have a religious belief.

[Sungai Pusat]

Nothing, everyone is functionally agnostic/sees themselves as such, even if they're spiritually very varied.

[Collectivist Germania]

I M M E D I A T E
C O N V E R S I O N
T H E R A P Y

[Neo-Libertine Hibernia]

Nothing, as most of our population are atheists, and we don't have any major religious-extremist movements.

[Alaroma]

In our Glorious nation, one of our concerns is to praise God. You would be considered strange, an oddball, uncivil, and uncultured if you didn't. God is in our Homes, Schools, and business. It wouldn't be long for your to be outed as an a Atheists. While not illegal,it's heavily discouraged.

[Moon Japan]

Nothing will happen

[Laxaria and Sakria]

Get ready for a lot of proselytism from Christians, Muslims, and the minority pagans You'd get a lot of criticism. However the deeply-religious populace would strangely leave you alone, for as long as you don't propagate atheism.

[Dernland]

Heh, that's cute, you think you have a choice.

In all seriousness, neither the government nor The Church requires one to believe, though you may be locked out of certain advancement options in various career fields (such as becoming a fully initiated Brother/Sister within the Military, or to ascend into the upper echelons of the government) if you do not swear to uphold certain traditions and beliefs.

[Tsunshun]

You'd be given an odd look, and people would continue with their day. Kinda confused on why someone would say something obvious in the first place.

[Breveten]

Soft chuckling at the ignorance. We who have seen the light of the trees know well the existence of the maker, as we stood at the birth of creation and sang with Him into being all that is.

[Weabooea]

Everyone would ignore you, except for the many government spies who would wonder why you would have to state that aloud. (Is he trying to convince himself, maybe he seeks to fool us so he can plant the seeds of religious lies in our schools.) and then they'd spy on you for a few days.

[Soyouso]

You are legally allowed to be a Soyousian Athiest, but here we have a cult that likes to sacrifice nonbelievers for agressive blasphemy, and the leader is part of it and one of the most devout members. You maaaaay want to run before the cultists set up an appointment to throw you into a volcano, or you could just politely say no to the door to door cultists asking if you would like to learn about our lord and master Flippy. Or learn about or lord and master Flippy.

[The Viare Isles]

Publicly? You'd be disqualified from holding public office, serving in the military, and if you're not yet a citizen you'd be disqualified from gaining citizenship. You could also potentially be marked as a Religious Dissident on your National Residents' Record under the V-C Unity Act 2004, which would make it difficult to achieve anything that requires a background check.

Privately? You would likely be spat on and, if you're unlucky, reported to religious authorities, resulting in an investigation which would lead to the above public consequences.

We don't suffer unbelievers and closet satanists like these lightly.

[United Socialist Ecuador]

Nah My nation is 50 50.
50% Religious
50% Atheist.
So...
Just don't ruin the balance and you will be ok.

[Brisketistan]

Assuming you're not an "In-Your-Face" disproving kind of atheist, most folks wouldn't give more than two tugs of a rat's tooth. Except maybe the Mormons, they'd probably give you shit for it.

[PT Belts]

Master Sergeant would tear you a new one. Mainly because you'd be speaking when not spoken to.

[Commonwealth of Rosewald]

Approximately 6% of the population is atheist or agnostic. Rosewaldians have complete freedom to believe or not believe whatever they want.

[Sillica]

Who cares...

[Technno]

Well, if you are human you will be follow the Technno's Order anyway, no matter what believe or not you follow you still subjugated by ubercybers. But we don't like human's religions, in fact we don't like any religion.

[Scharrath]

The demons would laugh at you.

[Gaozu]

Congrats, you have basic common sense!

[Shikinami Asuka Langley]

Laugh at you for thinking anyone cares in the slightest what you believe.

[Abidawe]

Nobody would care, if you made a big to do about it people would just think you were fishing for attention

[The Worker Utopia]

The nation most likely wouldn't give a damn as most are secular themselves and even those who aren't atheist, aren't exactly very religious.
If anything the nation would try to convert you to FULL COMMUNISM