Nilly, my "establishing scene" post happened only in my head but not on paper.
The establishing scene is the scene that establishes who your characters are and why they matter. In Buffy, it's the bit in WttH where Buffy is lured into a dark alley and then kicks the vampire's ass. It's "Ohhhhhh... *this* is the movie in which the tiny blonde girl isn't the victim."
In Butch Cassidy, the establishing scene has a guy acting like a boor in a poker game, bullying the other player (Robert Redford) and accusing him of cheating. The other player just stays quiet and takes the abuse. Paul Newman is trying desperately to mediate, trying to talk the bully down from his escalating demands. After his last attempt, he says "Sorry, Sundance, can't help you."
The bully freezes; the power in the scene does a 180. All of a sudden the bully is very very afraid; this isn't some random poker player, it's the Sundance Kid. He backs down and Redford and Newman prepare to leave. The bully calls out "Just how fast are you?" Redford spins around, and in six shots shoots the bully's gun off his belt and propels it across the room.
So. Robert Redford is a famous gunfighter. He doesn't pick fights or go into them lightly. He and Newman are fundamentally decent men, but dangerous. And we're off!