Just to make sure we don't go down the drain, I will explain to themoreyoulearn:

(1) The noun дибил or дебил comes from дебильность, which means "cognitive debilitation" -- so etymologically, it's more or less similar to the English "RE-tard."

(2) The obscene word бл*дь does literally mean "whore," but in most contexts one should freely translate it as "holy sh!t" or "Jesus t!tty-f*cking Christ" (©2004 Team America: World Police) or "for f*ck's sake," etc. -- in other words, it quite often has NO grammatical connection whatsoever to any other word in the sentence, nor does it have any literal reference to prostitution or slutty women. (But it's always obscene!) So one could translate that sentence you gave by moving the blyat to the front and saying, "Holy sh!t, you're f*cked in the head, retard!" Or you could "creatively render" the blyat as "You're f*ckin' f*cked in the head, retard!"

(3) Russians sometimes act like they're the Jedi Masters of Cussing ("There's no мат in the whole world as filthy as our русский мат," etc.), but in practice they can be surprisingly shy about the subject, especially when teaching these words (or hearing them!) from foreigners. Bear in mind that the most obscene Russian words all have to do with sex -- and many Russians still blush at saying секс out loud, in public, and prefer to say половой акт. For this reason, I strongly advise that when you happen to learn Russian cuss words, you should not use any of these dirty words yourself in an attempt to convince Russians that you're a bad-ass mofo.

(4) If you absolutely can't resist the urge to cuss in Russian, it's better to use euphemisms such as блин, ё-моё, пипец, and so forth -- this way, you can still "show off" your knowledge of slangy, slightly rude Russian, without causing huge offense. Trust me, Russians won't think that you sound like some prissy Ned Flanders type if you use блин instead of бл*дь. (Note that these euphemisms are still rude, but are nevertheless a lot milder than the words/phrases they replace. I would guess that they are at approximately the same level of inappropriateness as the words "fart" or "bullcrap" or "this sucks" in English.)

Edited to add for Russians: Be advised that using the English noun "rétard" to describe someone who actually has Down Syndrome or autism or any other cognitive disability sounds EXTREMELY offensive (and "lower-class") to 100% of educated English speakers, while the formerly-polite adjective "retárded" for such individuals is now considered old-fashioned and therefore may offend some people (Cf. "Negro", "Chinaman", "Jewess" -- all these were polite in the past, but now rather offensive).

So I strongly advise that you NEVER EVER use these words in a literal way when conversing in English. On the other hand, the metaphoric use of these words for people of normal intelligence who are behaving stupidly is a bit more controversial -- some English speakers take offense at this usage, others don't.