a      =    not, without

 theism    =    belief in the existence of a god or gods

Atheism means that you are WITHOUT belief in god or gods. Plain and simple.

The confusion with the term arises because of an old, incorrect definition that described atheism in its simplest term as the "belief" there was no god (Some atheists do believe that). I'm sure it wouldn't take long to Google and find the old definition. It is simply not accurate, however, and there's a better understanding just up ahead.

As pointless as semantics are..

It's not pointless here as it really does fall to technicalities to understand this and as _underwater pointed out, to decide where the burden of proof lies. Atheists can believe whatever the hell they want to but those beliefs would be completely separate from the simple state of being atheist, even if one of those beliefs were that there is no god.

That would make you a that-guy-owning-lambos agnostic. To be a that-guy-owning-lambos atheist, as it were, you'd have to believe he didn't own lambos.

Not quite. If you are without belief in the claim there's a guy with 10 Lambos (Lamboism) then you are an a-Lamboist. If you say, "I am without belief in Lambo guy but I don't or can't know for sure" then you are an agnostic a-Lamboist. If you reject the Lambo claim and you say you know for sure he doesn't exist then you are a gnostic a-Lamboist.

You unthinking atheists

Try to keep up with us "unthinking atheists". We have pictures, if it makes it easier for you.