HI,
With the odd exception, most acronyms or abbreviations should be obvious, from the thread that the post in question has been placed in.
For example, when the LORD OF THE RINGS series came out, most of the films were abbreviated to:
LOTR - Lord Of The Rings
TFOTR - Part 1: The Fellowship Of The Ring
TTT - Part 2: The Two Towers
TROTK - Part 3: The Return Of The King
I agree, that it shouldn't be difficult to write out some abbreviations in full, but then that's the point of an abbreviation - to save time writing the whole thing out.
If you can point to examples that aren't clear to you, then people on the Forums will happily do our best to help you work out what the abbreviations mean.
EDIT: I'll try to work out some of the abbreviations you mentioned in your original post. Their meanings will depend on which thread they were posted in, however!:
TC - Thread Count
KoOTR - Computer game: Knights Of The Realm? or Kingdom of The Realm?
GC - General Chat
OP - Original Poster / Original Post (the person who started the thread, usually)
Pooch