From 1966, with James Mason, Lynn Redgrave and Charlotte Rampling. The look on Redgrave's face when Mason says, "Georgy, I'd like you to become my mistress," is priceless.
By Hal David and Burt Bacharach, from "Butch Cassidy and the Sundance Kid", George Roy Hill's classical Western from 1969. Who can forget the line, "Hell, the fall will probably kill you."