With this picture from WHY Outreach with the fictional character of "Dr. Bob Palindrome", this cartoon shows how atheists may feel so mature, rational, free-thinking and enlightened but their actions say the opposite. But as said, by their fruits they will be known and remembering how some atheists behave, it can be shown by their penchant for mockery, name-calling and deliberate misrepresentation.
I would admit it does get annoying and it's very easy to lose one's temper when one is mocked, called names and/or gets misrepresented. Taking a closer look at why such people do what they do with their unethical activities, it really shows a lack of confidence in their own worldview. The more I look at their behavior, the more I am reminded of what Romans 1:21-25 has to say about them. They know that God exists but they don't wait to retain knowledge of Him in their minds. Instead, they became ungrateful for Him who made them, they want to govern themselves and the results are ugly. It's no wonder a lot of those who support same sex marriages are atheists which is against the natural order of God.