I don't disagree with you
You’re giving the other person a fake compliment, but you really think they’re an idiot.
My coworker said, 'I don’t disagree with you,' when I told him the report was nonsense.
My mom said, 'I don’t disagree with you,' after I told her I was moving out.
My friend said, 'I don’t disagree with you,' when I told him he failed the test.