Can't Change The Spots.
Scene: Last night at my local grocery store. I'm standing in line with my purchases, thumbing through a trashy magazine that I don't intend to buy. I overhear Grocery Manager and Cashier talking about a customer they just had in line.
Cashier: You know what? I am sick and tired of that guy treating me that way. He talks to me like I'm an idiot - I can't freaking stand him.
Grocery Manager: That guy? He's a jerk. He'll always be a jerk. He's been coming here for years.
Cashier: I'm going to tell him off the next time he is in my line. Let him know he can't treat me that way.
Grocery Manager: (squaring off his shoulders and looking down at the Cashier) Nah, don't bother. I went to college. I'm educated in the ways of these kinds of people. I know his type, so don't waste your breath. You can't get a lion to change its spots.
Cashier: (staring blankly) What?
Grocery Manager: A lion ... you can't get that thing to change its spots.
Cashier: I think you mean a leopard. Right?
Grocery Manager: (grunting) Hey, you've got a customer here. Start ringing, okay?
I laughed so hard that I ended up buying the trashy magazine by accident.