Past participle: when others see through your attempt to pass off AI slop as your own writing and thinking, usually due to carelessness.
Ex.: “My teacher caught me sloppin’! I turned in my paper and forgot to remove a sentence at the end where ChatGPT asked, ‘if you like, I can complete one last pass of copy-editing.'”
“Sloppin'” can be used on its own to describe this lazy and deceptive use of AI, e.g., “I don’t read emails from John, he stays sloppin'”.
The phrase “caught slippin'” lurked in my head; I heard it in early 2000s hip-hop and then from the high school students I taught in the late 2000s. It describes someone suffering consequences after letting down their guard or being careless.
Then AI slop – and the phrase “slop” to describe it – became ubiquitous. Put them together and you get a phrase I needed.
As far as I can tell I’m the first person to write this phrase. I tried Googling it, in quotes – and I caught Google sloppin:

Bullshit, it’s not a “colloquial variation” – the only hits are from a TMZ post about reality TV actors “caught sloppin” each other’s mouths (ew).
A friend told me recently that he had been on an email chain at work where his colleague started a message with, “Hi [recipient name].” I’m not redacting that: the colleague left in the bracketed placeholder from ChatGPT.
Boom. Caught sloppin’.