This is a great one. Another is when Mr. Brennan (William Devane) tells Slocum about the "rules" a cowboy lives by and finishes the conversation by telling him " and before I leave, I will kick your ass!"Monty, "Rudy you can't have no idea how little I care"!
Sam Elliot as Conn Conagher-
Laban Teale "Who gave you the black eye?"
Conagher "Nobody gave it to me son. I fought for it."
So many great ones from Lonesome Dove and Tombstone already mentioned.
My favorite Duvall speech is in Secondhand Lions when he is about to fight the punks.
"I'm Hub McCann. I've fought in two World Wars and countless smaller ones on three continents. I led thousands of men into battle with everything from horses and swords to artillery and tanks. I've seen the headwaters of the Nile, and tribes of natives no white man had ever seen before. I've won and lost a dozen fortunes, KILLED MANY MEN and loved only one woman, with a passion a flea like you could never understand. That's who I am, NOW GO HOME BOY!