I know it like the back of my hand

I know it like the back of my hand - Interesting but which hand are we talking about, left or right? They are different. Do political leanings come in play if there is a choice? Besides whoever spent time becoming thoroughly familiar with the back of their hands? Is the back of your hand the same as it was a day ago, a month ago or a year ago? So what are you telling me when say you know something like the back of your hand. Your telling me that you don't know your ass from a hole in the ground. Enough for anatomy.