In general, downvotes reflect people's interest in seeing less of the thing being downvoted. Accordingly, I'd recommend making fewer jokes of this sort in the future.

More specifically, I suspect the SMS-shorthand message style plays a role here, as does insulting Fyrius for asking a question.

Will somebody please tell me why this is being downvoted so heavily? I was just making a joke...

Your joke was poorly calibrated to this audience. (Further, the audience to whom that joke is well calibrated are obnoxious prats.)

TheOtherDave's description of why the joke doesn't work here is spot on. In some (most) circumstances it is possible to score cheap social points at the expense of anyone who admits ignorance. That is discouraged here. You can still get away with it (unfortunately) but at least have to do so with a modicum of subtlety.

Another factor is that things being "too deep" usually just means they are bullshit. It is the "deepness" that should be penalized, not those people who admit that the Emperor Has No Clothes!

Downvotes are basically "no"-answers to the question "would I want to see more of this here?" And even though I got your joke, I certainly would not want this place to start looking more like that. Both due to style and due to the fact that it's noise (doesn't have anything to say).

On the other hand, upvoted you for politely asking for feedback.

Useful advise: on the internet no one can tell when you're being sarcastic.