not you
incredulous
the one-line answer
Addressing someone in disbelief at what they just did.
Not you is used when someone does something unexpected or bad enough that you need to address them directly but without naming them. 'Not you doing that.' It is accusatory or surprised.
mainstream
Your coworker might use this word.
01 / in the wild
hear it move.
roast
not you sending that meme to the work group chat.
I cannot believe you specifically would send that inappropriate meme professionally.