Can An Atheist Be Sanctimonious?

According to the Dictionary app on my phone, sanctimonious means "excessively or hypocritically pious." I suppose these days that I most often hear the word used by atheists to describe religious people. Let me give you the typical scenario.

Someone asks a question regarding the religious person's belief system. In this particular case, let's say that the query involves the morality of homosexual conduct. Let's also assume that the religious person's beliefs would consider such conduct to be sinful. The religious individual provides the answer, "My faith teaches that homosexual conduct is sinful." The atheist, whether they were the questioner or not, takes the conversation on a path of mockery, perhaps mentioning flying spaghetti monsters or invisible men in the sky or some other such caricature of the theist.

This is a tactic currently being advanced by some of the more prominent atheists in the world. I find that it is often coupled with accusations that the theist is some sort of smug, morally superior jerk. Again, these accusations are usually in response to nothing more than the theist providing a description of what they believe. Perhaps they elaborate. Perhaps they don't. The discussion unfortunately will proceed in the same direction, regardless.

I know plenty of atheists. Many of them are not jerks. However, I've noticed a growing tendency amongst even them that leans towards malice in discourse. When I bring this up to my colleagues and friends, they are usually somewhat embarrassed and understanding that such comments are out of line, but they fail to provide a reason for why the fuse is so short. The weird part is that they don't see how they are behaving exactly in the sort of manner that they claim to hate so much in Christians and other religious.

Smug condescension doesn't win folks over to your point of view very much, so I would hope that Christians wouldn't act that way. I'm not even sure atheists want to convince anyone of their perspective. At least the Christian jerk is ostensibly trying to convert somebody. Even if their argument is as simple as "you're going to burn in hell," it's still an argument based on a hypothetical threat of damnation. The atheist jerk doesn't even try and argument anymore. As Richard Dawkins advises in the above link, the atheist's only participation is to mock the other party. If that's the case, why even talk about it in the first place? And, in the case where the atheist asks the initial question, why ask if all you're going to do is call someone names?

Notice that nowhere in here do I claim that Christians are immune from being sanctimonious d-bags. I freely admit it. The difference is that there often seems to be a bizarre presumption that atheists can't be sanctimonious d-bags.

Edit: Upon further reflection, it seems to me that the atheist is not actually sanctimonious at all since he does not even have the appearance of any sort of piety. Given the above definition, he is therefore only a standard-issue d-bag. My apologies for any confusion the previous paragraph might have caused.