If you want to know what atheism is then ask an atheist

I AM NOT AN ATHEIST 

I saw this the other day and I immediately thought that strawmen are not your friend.  A strawman is a logical fallacy when you criticize someone for an argument they do not actually hold.  Quickly let us look at this.

The belief 

OK, we have to stop already.  While I consider atheism a "belief"  and a religion. Many atheists consider atheism not a belief, but a lack of a belief.  The saying typically goes something like: if atheism is a belief/religion then not stamp collecting is a hobby.  Some might say, "I do not believe in a God."  For many atheists the idea that atheism is a "belief" is not something they argue.

Perhaps here we should also define atheism.  Dictionary.com defines atheism in both ways.

1. the doctrine or belief that there is no God.
2. disbelief in the existence of a supreme being or beings.

Atheism simply has to do with theology or lack of theology.  There is not embedded in the definition an origin of the universe or an acceptance of a scientific view point.  

that there was nothing and nothing happened to nothing 

What is nothing?  First, I may need to do more research, but most of the atheists that I can remember are materialists.  Nature is eternal.  Those that do not believe that nature is eternal are agnostic on the subject.  They do not believe in an ex nihilo creation.  Maybe some do, but I do not think that any atheists that you can name believe in such.  

Also "nothing" in physics can produce something.  Empty space has stuff in it.  Some atheists mean this when they say "nothing".  Also the Big Bang is something, a singularity extending through all space at a single instant.  You can say where did the singularity and space come from?  You might get some answer about a multiverse, but most would not say from "nothing". (meaning no spatial or temporal dimensions, no particles, no energy, no force)

and then nothing magically exploded

Magic?  The point seems to be that there can be no natural explanation for the Big Bang, so an atheist must invoke some unnatural or supernatural explanation.  I don't think that this is so much of a strawman, but more of sarcasm.  Obviously with no supernatural source for fairies, goblins, ghosts, witchcraft, miracles, cursings, blessings there is little place for magic in an atheism.  

Exploded?  I presume that this is in reference to the Big Bang.  Big Bang is a little bit of a misnomer. In the Theory of the Big Bang the singularity did not explode in a conventional sense, but it was rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Universe expanded increasing the distance between particles.  

for no reason,

Apparently natural law is no reason?  It would be true to say that most atheists do not believe in supernatural  reasons, but as long as time has existed there has been a macro cause and effect.  

creating everything 

Yeah according to Big Bang, quarks arranged into atoms clumped together to form stars which their own mass caused the single proton Hydrogen to fuse into Helium.  Still all of this occurs under natural law.

and then a bunch of everything magically rearranged itself for no reason whatsoever into self-replicating bits which then turned into dinosaurs.

There is that M word again.  My problem with strawmen is thus:  It is OK to joke as long as everybody gets the joke.  Not everyone believes this to be a joke.  More and more we seem to be inventing arguments for our opponents to fictionally hold.

1. We have enough to discuss without inventing arguments that our opponents do not even hold.
2. We lose trust when our students find out that their opponents do not actually hold said argument.
3. We lose trust of our opponents when we ascribe things to them that they do not hold.

PS - I am a little troubled by the use of the word "magic".  One, there are some notable atheists that are magicians (Penn & Teller, James Randi, Rebecca Watson) however most atheists do not believe in supernatural forces.  Two, most atheists argue that natural forces are sufficient to explain the universe, however most of the people that I have seen using this image believe that natural forces are insufficient.  In fact the tone of the text seem to ridicule atheists who believe that natural forces are sufficient.  This seems ironic to mock atheists for needing the magical/supernatural forces that you hold are necessary.  Three, this seems to set up a false dichotomy.  Most Christians also believe in the Big Bang, Abiogenesis, and Evolution.  They may also believe like Behe that nature was guided or needed a little miracle here and there.  This is the doctrine of the Catholic Church and other Christian denominations.  Atheists like most Christians believe in the Big Bang, just some believe that God helped it along.