Sarcasm

I don't get sarcasm.
Or, rather, while I understand the theory behind sarcasm and vaguely comprehend its utilitarian purpose, I often do not recognize sarcasm when I encounter it.
Since "not responding appropriately to sarcasm" is one of those classically, stereotypical signs of Asperger's Syndrome and other Autism Spectrum Disorders, I just want to pause here to remind us all that not all autistics have trouble with sarcasm.  But some of us do.  And I'm one of them.
Basically, I think I discovered why I don't get sarcasm.  In a discussion this evening, I got upset with somebody for using sarcasm and subsequently confusing me.  I, somewhat flustered because I didn't understand what was going on, shouted at this person and nearly started crying.  I was simply befuddled by his words.
When he asked why it was that I disliked sarcasm so much, I explained this to him: sarcasm confuses me, and I don't like being confused.  What I said was something I say often: "I mean what I say and I say what I mean.  And I expect other people to do the same thing."
What I was trying to explain is that I believe in language, and I just intuitively trust that words that others use will be true and will accord to their accepted definition.  I just assume that the words that other people use mean what they should mean.
I think that's why I don't get sarcasm.  Because sarcasm requires usage of words in order to convey a different, often opposite, meaning.  And that's confusing.