Is it irrational to believe that no God or god(s) exist?

Why or why not?

The real question is whether or not it is rational to believe that they do. One needs a reason to believe something not the other way around.

As God(with a capital G) is another way saying "The supreme and ultimate reality", to deny God is to embrace nihilism which is self defeating and irrational.

I disagree whole heartedly, as the subject of God and even the existence of God is even moreso a philosophical question than a religious one. Historically speaking, God has been the subject of much philosophy. 

That said, in many cultures and languages the distinction between religion and philosophy is practically if not outright nonexistent.

We would need a reason for believing that God does not exist.

On the other hand, we would not need a reason for neither believing nor disbelieving in the existence of God or gods.

Ignoring the snide remarks, this is also actually the first post I've seen you make that has good, useful content.

Perhaps the first place we begin is by defining what the word "God" means. 

Perhaps the better place to start is to determine what's minimally necessary to falsify the view that no God or gods exist.

What do you think?

Do you need a reason to believe that universe creating pixies do not exist? Do you neither believe nor disbelieve in leprechauns? I have a hunch that your default position in most undetermined cases is skepticism and that the only thing you "need a reason to believe doesn't exist" is in the case of god(s).

Yes, you do need a reason for believing that universe creating pixies do not exist. 

No, I disbelieve in the existence of leprechauns.

My default position is neither belief nor disbelief, especially prior to consideration of the claim. Once the claim has been considered, my "default" position is determined by the relative amount of evidence I have at my disposal for and against the claim.

Do you listen to "the atheist experience"?

And what reason do you have to disbelieve in leprechauns?

I do.

Yes. The term "pixie" typically refers to a being that is "small and humanlike in form, with pointed ears and a pointed hat." Since pixies are comprised of physical characteristics, and since our best evidence indicates that the physical universe expanded from an infinitely dense point 13.7 billion years ago, it is unlikely that a pixie or any physical being existed prior to the big bang in order to cause the big bang.

Leprechauns are described as "solitary creatures who spend their time making and mending shoes and have a hidden pot of gold at the end of the rainbow." 

A leprechaun, along with any other physical being, exists at a particular coordinate. There is no particular coordinate at which a rainbow ends.Therefore, a leprechaun cannot place anything at the end of a rainbow and the claim is false.

"You'll never swim out to the horizon , and you'll never reach a rainbow's end. The visibility of both requires distance between object and observer."

Universe creating pixies wpuld exist outside of the physical universe of course and leprechauns are invisible. Clearly we would not expect any evidence of them (beyond the existence of the universe itself of course in the case of the pixies) so if no evidence is what we would expect and no evidence is what we see hiw is thus functionally different from believing in any god(s) for whom we would expect to find no evidence of?

Perhaps a more fitting question

Can the belief be rationalized?

Since a "pixie" is defined according to its physical characteristics, a "pixie" cannot be non-physical. This would be a violation of the law of identity. 

Leprechauns are described in terms of their physical appearance and therefore cannot be invisible, nor is invisibility a part of their defintion.

Evidence against something is encompassed by lack of positive evidence. So while 'no (positive) evidence' of pixies and leprechauns is true, the evidence against pixies and leprechauns is the important piece missing in that statement. 

Evidence is just information indicating whether something is true or untrue. I haven't seen any objections to the existence of God in the case of pixies or leprechauns.

Perhaps. Something being rationalized doesn't make it rational to believe though, does it?

Precisely, it does not.

Then the problem is with my examples not my premise. How about the invisible undetectable dragon whose breath is holding up my garage? Do you believe in that? The evidence of course being that my garage has not fallen in.

Analogously, I would think you would ask if they believe that such a dragon does not exist.  

Sagan's dragon is also a violation of the law of identity and therefore doesn't exist. 

"Dragon": "a mythical animal usually represented as a monstrous winged and scaly serpent or saurian with a crested head and enormous claws."

When you refer to the concept of a dragon and then say that it does NOT have the characteristics that make it a dragon in the first place, it's a violation of the law of identity.

So not only do I not believe that an invisible dragon lives in my garage, I strongly disbelieve it. 

Not a dragon then just a garage spirit. 

What do you mean by "spirit"? Like just an observing consciousness?

I'm not sure what it is, just as you are not sure what the god(s) you are proposing are.  It is an invisible formless spirit that keeps my garage from collapsing. It has attributes such as preserving garages and being undetectable.

Do you feel that is more or less rational than the idea of a garage spirit? And is it more or less rational to believe in one or both of these spirits than to believe in some god(s)?

Rational is not more or less to my way of thinking. It either is or it isn't.

Ok so is it ir isn't it?

One of the defintions of "god" is "a powerful ruler"

Vladimir Putin is a god? Donald Trump? Pope Francis?

Atheism, nihilism, anarchism...

Somehow all very much related in their thinking! Denial of reality ties them all together.

I've always described God as a consciousness. 

As for whether there is a being or spirits in your garage or anywhere else we have no evidence of that. I think that if some entities walked the earth they'd be somewhere more interesting than your garage. So I'm gonna go with disbelief on this one too. 

What precisely makes belief in god(s) more rational than a garage spirit? Just because you "think" they would have better things to do? Claerly they don't or my garage would fall over. Seems as rational as a belief in any entity/conciousness/being that we have no direct observable evidence of to me.

Because (1) existing and (2) existing in a specific geolocation, such as a garage, is more prone to error than just (1) by itself. 

Yes, I am speculating that if there's a spirit realm on Earth that the spirits would be someplace more interesting than being in your garage. 

God's existence has evidence unlike the claimed spirit in your garage.