KKR,
I think it is possible to inject some humour into a post, but the tricky part is doing so that:
A) everyone knows it's a joke. And assuming we are talking about a vigorous debate thread, that should include not just your buddies or routine opponents who have some feel for your written sense of humour, but particularly people you either have bad history with on the MB or with whom you are engaged in vigorous debate. And,
B) there is not an obvious (although perhaps unstated) butt of the joke, except maybe yourself.
Sort of like I said before, if you have pre-qualify a comment that it's just a joke, it's probably better to skip it entirely or re-phrase it so it doesn't need the pre-qualification. For every joke that defused a tense situation with laughs all around, there is probably another one that made one side or the other feel they were being mocked
As always, my thoughts only, and your mileage may vary,
Mike
P.S. By the way, the whole mileage thing was just a joke to lighten the mood. :)
P.P.S. Oops, now I just violated my own rules by having to qualify that it was a joke.