I wonder how far back that dates. At what point in history were humans still throwing rocks at birds trying to get a meal? And why does it still convey a message?
We used cow hocked referring to horse conformation. An idiomatic expression? but I don't know about hack kneed. Maybe I should stop doing these tangents.
Don't stop. I just learned a lot by looking up those expressions. You've not gone off the deep end yet.
Hold your horses. Y'all are silly as a goose and will paint yourself in a corner sooner than later or when pigs fly.
The first time I heard that expression was when I was 20 years old and managing a Hess gas station (the Odd/Even Crisis years.) I heard it from the District Manager, a guy who was full of his own crap. It still grates due to the source-of-origin, not because of its triteness.