The "I was going to say X but I didn't" joke seems common in the CS/computer community. I find it vaguely irritating, because you're saying something you know you shouldn't be saying, as evidenced by distancing yourself from the statement. I was going to downvote, but maybe I can add to the discussion instead.
I have noticed that many people here think that jokes do not add to the quality of discussions. A joke is just one of several ways of introducing non-direct references to arguments (I think I can call them "hints"). I had a hypothesis that people may not like such hints which, after all, may be culture-dependent. So I tried other ways of hinting and found out that they do not seem to evoke such a hostile response. So it must be something else, but I am not sure what exactly. Another possibility is that people may be offended at jokes, even inoffensive ones, but this is not something I would like to test.
As far as rhetorical devices are concerned, there are many of them that may be used in a discussion without detracting from it. HN does not need to be dry and often is not.