They cannot conceive of what you have just told them, and they immediately begin to rationalize it in their minds.

If anyone tells me I am not really an atheist, which has never happened, I will have to concede that technically I am more of an anti-theist at this point.

Because they do not understand what an Atheist really is. Too many people are using Agnostic as a comfort term to not insult believers.

Cognitive dissonance. Your convictions don't align with theirs and their reaction is to correct that, in a way convenient and soothing for them.

Every one even the religious, is an Atheist in reguards to other gods.

I think believers interpret agnostic as being unsure instead of not knowing. If you are unsure, there is a chance they can bring you back into the fold and in saving you become the hero. And everyone wants to be a hero. By being atheist you deprive them if the chance to be a hero.

They say that in order to feel better about themselves.

They must not believe its possible to be sure about there not being a god, and this is their cutesy way of trying to force open your mind to their nonsense. in a way theyre correct, almost every honest person in the world would be an agnostic but that doesnt mean you can't also be atheist. They just don't know the definition of atheist or that the two arent mutually exclusive terms.

I would at that point tell them theyre changing the subject. I believe in no gods or theism so I am atheist. I am without absolute knowledge of everything in the universe, which would be necessary to claim certainty either way so I am also agnostic. I am an agnostic atheist. The premise of no knowledge and no evidence also will lead a logical person to have no belief. so sit down and quit trying to tell me about what is known when it supports my lack of belief in the first place.