This is not meant to offend, but it seems to me that you've just experienced an
everday miscommunication.  I'm surprised that it affected you so much to write
about it.

I wonder why you gave him that much information?  I assume you've been to Radio
Shack before, and you know that the salepersons working there do not need to
have any knowledge of electronics to work there.  When asked, "What kind of
wire?"  You probably would have gotten the information you needed by only
telling him the information he needed, "Coiled telephone wire" would certianly
have been sufficient.  It wasn't like he was asking you what you were using it
for, or why you chose it.  You gave him some parameters about the wire (coiled,
isolated, handles 6v @ 800mA) a suggestion that might work, and a reason not to
use another type... But that left the conversation wide open for him to inject
his own knowledge.  (never give a salesperson the oppurtunity to choose what you
buy.  If you don't know, ask questions and study it, but make your own choice!)
I understand that he shouldn't have been trying to dissuade you from buying a
specific product, but the miscommunication is clear:  He thought you meant 800mA
per strand (so he was absolutely correct in what he was saying, as far as his
understanding of your needs were, and the product you had suggested).  At that
point both of you became defensive and weren't trying to resolve the issue.  (a
good example of a lose-lose situation)

But it's the age old problem with communication.  Too much information is just
as confusing and useless as too little.

Anyway, it really doesn't matter - you can buy coiled phone cords without
questions from nearly any hardware and most large grocery stores...

-Adam