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.
I learned this as medical short hand back before electronic medical records were everywhere. Except I used f/u instead of f/up. This phrase went in almost every single case note every day so I used the short hand A LOT. It still sneaks into my writing sometimes.