>I'd like to know when and how to use "the hell", such as "what the hell are
>you talking about?". How offensive and rude do Americans feel about it? I'm
>wondering because I think at least I should be prepared to use it when the
>time comes.
>

It is abundantly clear to all that there are differing styles of
discourse in every language, and that there are distinct contexts where
each is appropriate and others where it is inappropriate, as judged by
the participants in those contexts.  We should all agree that use of
language inappropriate to a particular social context, in speech or in
writing, is a faux pas, and can, depending on the nature of the
situation, have serious repercussions.

That said, further opinions about the degradation of profanity, The
Decline of Western Civilization, or the Heartbreak of Psoriasis are
one's own responsibility.  The poster, like every mature language
speaker and learner, takes responsibility for his own language use, and
merely asks a straightforward linguistic question.

The question seems to be how "the hell" is used, and so far all the
poster has received is exhortations not to use the language as its
native speakers obviously do use it.  alt.usage.english should be 
able to do better than that.

To start with, "the hell" must be distinguished from "Hell!", or "Oh,
hell!", which are full utterances (traditionally, "interjections", the
last and least of the classical Eight Parts of Speech), the sort of
thing you say when you've made a mistake, had a mistake made for you, or
otherwise experienced the displeasure of Fortune.  They are
linguistically unusual in having no syntax -- "Oh, hell!" is a full
utterance (though hardly a 'sentence' - no subject, no verb, etc.) and
needs no further complement.

There are also some fixed phrases. "What the hell" is used to express
disregard for conventional procedure and precautions, in varying degrees
(the phrase has some of the same implications as "devil-may-care"). It
is usually a phrasal interjection, without further syntactic
ramifications:

   What the hell, let's just compile it now and see if it runs.
   The odds were 100 to 1, so I said what the hell, I'll bet it all.

This is sometimes spelled in eye dialect as "wotthehell" or the like.
Don Marquis's character Mehitabel in "archy and mehitabel" immortalized
this usage in the field of English (lowercase) letters:

   wotthehell wotthehell theres life in the old girl yet

"What the hell" is sometimes seen with an exclamation point, but should
not be written in this usage with a question mark (or pronounced as a
question); "What the hell?", often with multiple question marks, is
short for a true question, like "What the hell is going on?" or "What
the hell did you say?".

Another fixed phrase is "The hell you say" ("*The hey you say"),
expressing (often surprised) disbelief at the last thing the speaker has
been told. It can function merely to express shock, or as an active
challenge, equivalent to calling your conversation partner a liar.
Conventions vary, and one should not use this phrase in a speech context
without having heard it used there before, and understanding its
implications.

 (Note, parenthetically, that the use of the definite article with
  "hell" is in itself idiomatic; like "heaven", "home", "school", and
  in the UK, at least, "hospital" and "university", these are locatives
  pure and simple.

     If you say a bad word you'll go to (*the) Hell.  )

The other uses of "the hell", on the other hand, have plenty of syntax.
It appears to be short for "in the hell", which is also heard, along
with "in hell", though less frequently.  Both "in the hell" and "the
hell" are restricted to WH-questions, where they follow the
interrogative WH-marker.
  NB: either, but *not* both, of (in) and (the) may be deleted in these

    Who (in) (the) hell is that?
    What (in) (the) hell are they doing?
    How (in) (the) hell did she get invited?
    Where (in) (the) hell did he come from?
    Why (in) (the) hell did you do that?
    When (in) (the) hell is this rain going to stop?

This also  applies to embedded questions, which have different syntax:

    I don't know who (in) (the) hell that is.
    I don't know what (in) (the) hell they're doing.
    I don't know how (in) (the) hell she got invited.
    I don't know where (in) (the) hell he came from.
    I don't know why (in) (the) hell you do that.
    I don't know when (in) (the) hell this rain is going to stop.

"the hell" may not appear with just any WH-word; "which", for instance,
is out, though "what" is OK:

   *Which (in) (the) hell did he choose?
    What (in) (the) hell did he choose?

and "whether", since it represents a yes/no question instead of a
WH-question -- essentially being identical to "if" -- is also out:

   *I don't know whether (in) (the) hell he's coming.

In compound interrogatives, like "how big" or "what book", as in

    How big is it?         I don't know how big it is.
    What book is it in?    I don't know what book it's in.

"the hell" goes between the interrogative and its complement:

 How the hell big is it?      I don't know how the hell big it is.
 What the hell book is it in? I don't know what the hell book it's in.

("in the hell" is much less likely than "the hell" in this construction)

Pragmatically, "the hell" functions as an intensifier, usually
indicating at least surprise, and often unpleasant surprise, and there
is almost always another word in the sentence that receives contrastive
stress to indicate that it is the focus of the surprise.  Co-occurence
of other interjections and topic particles like "well" is also common.
The idea seems to be to mark the sentence strongly, iconic with the
strength of the emotion to be expressed.
(I indicate contrastive stress in capitals)

   Well, how the hell big IS it, then?
   Why the hell did you DO that?
   How the hell did SHE get invited, anyway?

"Hell" is considered by many (but not by as many as it used to be) to be
a taboo word, like "death" or "cancer". Therefore it spawns euphemisms,
which are words meaning the same thing as a taboo term, but considered
safer for bystanders by experts in word magic.  Frequently-encountered
euphemisms for "the hell" include:

   "the hey"        for the "wotthehell" construction only
   "in the world"   for the question construction only  (obligatory "in")
   "heck"           which may be freely substituted for "hell"

  --------------------------------------------
 -John Lawler                     More grammar
  Linguistics Program   University of Michigan
 "..and, who knows? Maybe the horse will sing."