My colleague wanted to diagnose a specific error code on his car himself, and Gemini told him that it's simple to do with an OBD2 dongle - he asked it about the details thoroughly, to confirm, and bought the dongle.

It didn't work. Gemini: "Oh yeah, that obviously cannot work, it's not possible to do it through OBD2" (paraphrasing)

It was quite funny to me, but a bit less so to my colleague.