Mine is OOO for Out Of Office. I always misread it in my head like a ghost and it takes me a few seconds to process. It also doesn't translate to speech—you have to say the whole thing.
Interested to see if others have similar acronyms they beef with.
YWNBAM/YWNBAW. Besides being transphobic (it's short for 'you will never be a man/woman'), I always automatically attempt to read/pronounce acronyms as if they were words, and this one sounds really stupid.