He doesn't know me from Adam's off ox

(Something I heard from NPR online radio)

"He doesn't know me from Adam's off ox."
(Oh my, I just noticed, there's a "Listen Now" link right below the title)

I'm more intrigued by this fact:(even though it's expected)
"Most of the journalists at that news conference had no idea what Clinton was talking about."
Why? Because ....
"It turns out the president was using a regional expression ..."
The merits:
1. Even well-educated native speakers (those journalists) don't always know everything.
2. So, it's really OKAY and absolutely normal if you(learners) don't know everything.
3. (thinking... thinking.. still thinking....)