pet phrases

"Y'all always run things in the ground," one of my more quiet and laid back and nephews has said. And it's true. We latch onto certain phrases and can't seem to let go. Some of them only we know the origin of and meaning behind. Others, we are not sure of where they came from or what they even mean. So why do we use them?
Good question.
I'm not sure.

Take: "for crying out loud?!" It's one the phrases I use most often yet I have no real idea what it means.

The same with "good gravy" and "good grief." Most all gravy is good, as far as I'm concerned but I am not sure any grief, so why do we say it?
I am going to collect a list of these pet phrases as I hear them and try to find their meaning. Just to educate myself. (and maybe a bit for entertainment value!)