they know God exists
If they did, they would not be atheists, so that's your own straw man of atheism, not atheism. You would convert them, if you had the convincing evidence and arguments.
angry at a Being who doesn't exist
An atheist indeed cannot be, because it would be pointless. They may be angry at the idea that if a deity existed, it would be an unjust one. Or at the irrational and bigotry justification arguments of those who attack people for not accepting to believe in the implausible. Or for not being the type of fundamentalist bigot you would like everyone to be.
literally right in front of them
Claims are not evidence. Human traditions are only evidence of human traditions. If you mean "creation", atheists acknowledge that reality exists, but do not fallaciously hastely jump to the fantasy that it's because of a particular deity of a particular people.
never question abiogenesis and macroevolution
This is also based on a false straw man. Science is self-correcting and about knowledge discovery. The discovery of evolution is not atheistic ideology, it is an actual discovery, an understanding made by following where observations of the natural world lead. Thus not only atheists accept reality. And if it was demonstrated to be false, with a better explanation for everything that biology and evolution explain, scientific knowledge would be updated. This is the reason you need a straw man, to deny all of this.
Because they are the pillars upon which their delusion depends on.
They are already living a lie to begin with, so a few more can't hurt; especially if they support their position, even without evidence.
What a terrible existence for them, is there any wonder they are so angry?
The above fallacies having been exposed, it becomes obvious that this conclusion is psychological projection and a necessary repetitive affirmation ritual to keep up the "us and them" rhetoric. In exploitative cults, this serves to radicalize, isolate and maintain victims, so they hopefully keep consuming the constant flow of propaganda and "services"...
And hey, this is the same Starr that advocates for genocide. So in this case, not only maintain victims in ignorance and control, but also to justify crimes against humanity. So "atheists" is revealed to be a loser's scapegoat...