Listening to angry atheist rants on the internet, one can detect a common sentiment or strain of thought running throughout. This sentiment goes something like this: "Atheists are inherently smarter than theists. All theists are ignorant and irrational because of the very fact that they are theists. Why bother engaging those stupid, dim sheeple in actual debate when they are so very, very ignorant?" This is why atheists generally come across as arrogant, whiny assholes.
It is also to remember that no atheist can understand lulz, as lulz, being a corruption of lol, means Love Our Lord. It is therefore impossible for a godless heathen to understand. No lulz may be had when you are too busy whining about how people who go out in the sun or shave are just deluding themselves and are too stupid to understand the workings of the universe which these fat, neckbearded slobs of course fully understand.
Another reason atheists generally come across as arrogant, whiny assholes is their long revered standard of ad hominem attacks on those with whom they happen to not agree. Rather than actually engaging into some form of serious debate with those silly theists and having the flaws of atheist positions shown as having no merit whatsoever, they instead attack theists and dismiss them personally based on presumably lower intellect, lack of scientific proof, etc.
Most of the time, however, an atheist will suddenly decide that it's a chance to fuck Christianity anally by saying "Where is your god now?" or "God does not exist" in ALL CAPS, at any event like 9/11 that an atheist can use to blame on God.
According to recent studies, there is a side behaviour to atheists online. If the religious person is an internet celebrity, some awesome artist, or anyone awesome who is Christian, the atheist will become a suck-up rather than an arrogant bastard.