I'm staying neutral on this one, but I can imagine that may people don't think this comment contributes much to thoughtful discussion of the topic. Promoting these comments, or even not downvoting them creates a culture where these comments become accepted. I can see a comment like this (if upvoted) easily starting one of those "pun trains" commonly seen on reddit.

I don't see anything specifically wrong with the ironic humor of the comment, HN does need to lighten up sometimes, but if we let one of these get upvoted... it will only lead to many more by precedent. The line has to be drawn somewhere. I personally wouldn't want to see a HN where each topic has 10+ "witty/ironic/humorous" comments. I go to reddit for that.

Your comment is at the bottom of a long page, which adds latency to it being reviewed. When it's in the positive it gets downvotes by people who didn't think it was very funny and people who don't want to encourage that kind of joking. When it's negative it gets sympathy upvotes, like the one I just gave you.

Although I think that XKCD comic is funny, I downvoted you for the reasons makeramen pointed out.