In addition to coldtea's examples, DK is particularly thrown around in competitive gaming communities, such as Reddit/Twitch around Dota 2 and League of Legends. I admit that it may not be as prevalent in the mainstream as other popular memes, but it's definitely there.
I've seen its use in those communities also. Usually the person applying thinks highly of their ability to identify a DK scenario. And, if someone professes not to understand something, DK is rarely applied in their favor. Bringing it up is effectively just a meaner way to say, "I think you're wrong."
