Now that you have grown out of that 'internet atheist' attitude, do you, despite being a lifelong atheist, find yourself annoyed when you see others exhibiting brainless atheist tendencies (i.e. those who come to atheistic thinking not via critical thinking but rather as though they have adopted a zealous attitude of anti-religion without really thinking about it)? I've had atheist friends whose atheism seemed to come about less as a result of critical thinking and more as a general, "knee jerk" reaction without much thought process to really exhibit how they came to their conclusions.
People coming to atheism from a knee jerk reaction doesn't bother me. I see Atheism not as an assertion or belief as such, no one is born believing things, the absence of belief is the default state, and when people decide they believe in something, they are convinced enough to reject their disbelief. I think it is valid for people to accept Atheism as a fiat, without requiring any justification.
It's not so much beliefs, but douche behaviours from the small set of 'fedora atheists' can be a bit annoying, where whenever there is any mention of God, they think it is their personal mission to argue, antagonise and generally be a pain, because it makes them feel good about how much more enlightened they are. Only seen those type on the internet though.
Hard to relate to what it would be like for Atheists in places like the US though. Where I live (NZ), secularism is the status quo, a majority of the population do not have any organised religion, and amongst young people, atheism is far less controversial than being religious, so the dynamic is a bit different. I think if I lived somewhere where religion was very dominant, like Bible-belt type places, I would feel quite a bit of hostility. A friend of mine who grew up in Missouri (intellectual, far left, sort of hippy type) said living in such a religious and conservative place was terrible for anyone that eschews the values of the place. So that could lead to some atheists being aggressive about their beliefs.
Nowadays, atheism is something I never really think about, and religion in general is completely uninteresting to me. When I was younger, I was entertained by the Christopher Hitchens / Richard Dawkings type thing of atheists vs religion. My opinions about anti-religiosity haven't changed, just it's not something worth caring much about.