Per dang's unusual request (https://news.ycombinator.com/item?id=9637459) and the fact that I have a convenient copy of the Hacker News database, I have made a chart plotting the usage of Rockstar and Ninja in comments on Who is Hiring posts:http://i.imgur.com/heXjYTW.png
It's mostly random how many instances there are of each phrase on a month-to-month basis; however, for Ninja, the number of instances is trending upward slightly.