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

[Durzan]

The citizens would shrug, ask why that is relevant to whatever conversation they were having with you (if it isn't actually relevant), and then continue with whatever they were doing beforehand. Religious freedom is a big deal here in the Empire, and that includes your right to non-belief.

[The Great Templar Order]

You would be burned at the stake.

[Pacomia]

You would be congratulated for following the true religion.

[Veria Republic]

Atheism is a freedom of thought choice that's protected by the Veria Republican Constitution.

[Veria Prime]

You would be detained, but not charged as atheism is not technically illegal. Veria Prime is working to criminalize non-belief very soon.

[Roma and Italia]

It depends on the time and place, claiming to not believe in God during the early days of the Empire (9th century) would probably get you burned at the stake.

If it was during 2019 however, a decent percent would not care, and some who do would not likely find you to be a bad person per say, but would still be judgemental.

[The Union of British North America]

Depends on where you are, but you won't be harassed or roughed up by police or government officials in most places. Other places are judgmental as you would expect. The general government and provinces are committed in principle and substance to freedom of belief, or in your case, non-belief.

[Etat Unitaire Francais]

Immediately detained, and forced to convert.

[The Sicilian State]

I’d feel very sorry for you

[Shizshow]

Not much friend! Religion is a way that people can gain followers and attention outside of the government, so atheists are actually considered patriotic.

[Winterwind Hinterland]

“Sometimes when I'm faced with an atheist, I am tempted to invite him to the greatest gourmet dinner that one could ever serve, and when we have finished eating that magnificent dinner, to ask him if he believes there's a cook.”
― President Ronald Reagan

[Hava and Bonzia]

You will get executed.

[Andrastia]

You would be in the majority. Most Andrastians are irreligious, including atheists. There are no repercussions from announcing one’s disbelief in a supernatural entity, but most normal people wouldn’t care enough to get involved at all.

[Albanian Iron Empire]

Killed, probably by the Emperor/Empress or one of the nobles, in a very painful ritual

[Purpelia]

People would wounder aloud why you bothered to talk about your religious beliefs. As if someone wants to hear about that sort of thing.

[Five Nations]

Nothing happens. Religious freedom.

[Menheru]

lots of "haha, same"s - that's about it, really.

[Bluelight-R006]

Most people will say, “Me too,” and the others would just ignore you.

[Chakyik]

You are free to be so, Chakyik is a secular nation.

[Onitsha Empire]

What would happen to me or anyone else if I were to mention that I were an atheist in your nation?

In Yakus, I/you would probably face an awkward stare as people try to figure out why it was important to mention such a thing, but most people do not care about religion. Some strongly conservative/deeply religious/countryside dwelling folk might try to convert you or condemn you to hell, but overall nothing much would happen. Catholicism is the largest religion in Yakus, followed by Protestantism, atheism, Buddhism, Daiwatai and Islam.

You will do fine. Queen Jessica is an atheist too.

[Varagr]

You would most likely be seized, your property confiscated and sent off to an execution grounds, where you would be hanged from a tree until noon.

[Indian Empire]

You'd actually fit right in with what the majority of the population believes.

[Thepeopl]

Yes, us too. Hadn't you noticed all the nude, cuddling ppl?

[Kinsmenland]

You'd get awkward stares. Most people don't give a damn and most people themselves are non believers.

[West Leas Oros 2]

People would be fine with it, and to a certain extent, that would be expected.