I'm not an atheist but this is weak.
Long argument, so strap in.
Imagine, if you will, a conversation with a theist and an atheist:
Theist: God is defined as omnipotent, omniscient, and a being of that which nothing greater can be conceived.
Atheist: There is not a God(s) and I refuse to believe in the foundations and conceptions of a God(s).
Theist: A God is omniscient, it knows about all. It knows every detail, large or small about everything. A God is omniscient because there is no other being or character that knows more.
Atheist: It is impossible for any being or character to know everything. This does not convince me to deny the conception of a God.
Theist: A God is omnipotent. A God can do anything. It has unlimited power and there is no other being or character that can interfere, or have more power than the omnipotent God.
Atheist: There is no being that can know all and do all. This is only an idea that is contigent upon our mind conceptualizing this. Therefore, since only our minds are creating this idea, there being a God is an act of our mind portraying flawed ideas.
Theist: God is that which nothing greater can be conceived. The very last concept in our ideas of what a God is; is that which nothing greater can be conceived. The concept of a God at that point is considered omnipotent and omniscient, as a result.
Atheist: Our ideas are a flawed conception and are fatal misunderstandings about our minds. The point in which nothing greater can be conceived is proof that our minds cannot affirm whether there is or is not a God.
Theist: The mere quality of a flawed mind proves that there is a concept greater than what we can conceptualize, thus being God. If our ideas are proof of misconceptions, then all conceptions must be contentious. As a result, no mind can affirm or disprove any concept.
Atheist: Correct. Our minds are flawed, therefore there cannot be any reason to confirm the exisitence of a God.
Theist: Exactly. If God can exist in the mind, then it can exist, therefore, you can only deny the existence of a God if you deny that there is nothing greater than which you can conceive. Therefore, you have to acknowledge one's concept of a God, otherwise you cannot deny what you are attempting to deny.
Atheist: There is no God. I have no argument as to why there is or is not one, and I cannot disprove one's idea without affirming it. To do so, I would have to deny my own ideas, meaning I would have to deny there is no God without a flawed argument. Since God is that which nothing greater can be conceived, then I would essentially have to be a God to argue there is no God.
Theist: There is a God because it is omnipotent and omniscient, thus being without flaws, and operating beyond our conception of our reality.