I don't think that downvotes necessarily mean that people didn't get the joke. If I see a witty one-liner comment to a serious story, my normal reaction is "Ha ha ha! Downvote." Or else I ignore it entirely. (And sometimes it simply _isn't_ very funny.)
I just don't think we need to encourage content-free comments here; there are plenty of places to go if you want to make fun of the news.
Then again, I moderate a site that's been accused of taking too hard a line on "fun", so maybe I shouldn't talk.
The problem I have is the inconsistency. I remember posting a sarcastic comment in a sea of sarcasting comments, then saying 'seriously though' and adding genuine content. Mine was the only comment that went gray. I've seen this stuff time and time again with other users - several comments of fluff, but only one gets pounded. What gets pounded in one thread gets rewarded in others - sometimes I'll post a snarky, devoid-of-content comment, hit post, and then wonder just how fast it will go dead and next thing I know it's really popular. It really is inconsistent, and that bugs me.
Well all comment voting systems are inconsistent just because it's tough to get a uniform number of views on comments over time. And now that vote counts are hidden, things are even more wonky in terms of what sees vote volumes.
But in terms of humor I think it's fairly straightforward: don't do it unless you think of something that's really fucking funny (and hopefully a little insightful). If it's funny enough you will get upvoted just by sheer force of charisma. If it's just marginally funny you will likely get buried, and I think that's a good thing, because a lot of people aren't as funny as they think they are, and you don't need to look beyond Reddit to see what a culture of one-liners does to a discussion forum. If it's just some simple pun then likely many of the readers already thought of it and don't particularly want to read it over and over again.
I just don't think we need to encourage content-free comments here; there are plenty of places to go if you want to make fun of the news.
Then again, I moderate a site that's been accused of taking too hard a line on "fun", so maybe I shouldn't talk.