Working at Frontierland, it was always:
CBJ- Country Bear Jamboree
TSI- Tom Sawyer Island
BTM- Big Thunder Mountain Railroad
Splash- The poor thing just never got abbreviated any further, even internally
SM- was always Space Mountain
TTA- the Tomorrowland Transit Authority
RNR- is common for Rock N'Roller Coaster
DDCT- the Disney Dreams Come True Parade
SADCT- the Share a Dream Come True Parade
MSEP- the Main Street Electrical Parade
Spectro- Spectromagic Parade
JII- Journey into Imagination
JIYI- Journey into Your Imagination
JII2 or JIIWF- Journey Into Imagination with Figment!
EE or ExEv- Expedition Everest
GRR- Grizzly River Rapids
KRR or more often "Kali"- Kali River Rapids
iasw- "it's a small world"
HOP- Hall of Presidents
IJA- Indiana Jones Adventure
And some less obvious ones...
CRH for Contemporary Resort Hotel
OKW for Old Key West
BWK for Boardwalk
NRG for Universe of Energy (say it out loud)
TAGBBT for "There's a Great Big Beautiful Tomorrow"
AE or EAE or ETAE are all the ExtraTERRORestrial Alien Encounter
WDRR sometimes took the place of WDWRR for Walt Disney World Railroad
LWTL Living with the Land
SWitNAF- Seas with Nemo and Friends (though it will always be the Living Seas to me

)
I've seen MV3D or M3D for Muppet Vision 3D, but rarely.
My personal favorite:
MNSSHP:BTYP The ever popular Mickey's Not So Scary Halloween Party: Boo To You! Parade
"put down the acronyms and back away slowly..."