A theist dilemma

[ApeNotKillApe]

I am an atheist, and I say God exists. I remain an atheist before, during and after making that statement. I do not believe in God, I say God exists.
I cannot believe in God and claim to be an atheist, I cannot be an atheist and claim to believe in God. 

When I, as an atheist, state that God exists, my statement is dishonest, and God does not approve of dishonesty.

When I, as an atheist, tell you that God exists, am I committing a sinful action? If so, why? If not, why not?