First film ever made about a bullied social outcast finally snapping?

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Possibly the first film, although the concept does bear quite a close resemblance to the Pirate Jenny segment of the Threepenny Opera (which also formed the basis of Von Trier's Dogville and may have made it into a film adaptation before Carrie). Whether King was familiar with that when he wrote the book I don't know. Really, though, the idea of someone who seems to be powerless (but isn't) being pushed and pushed before they finally snap goes right back to The Odyssey (the ending of which is, I'd say, pretty clearly echoed in Carrie - enclosed space etc.) - which suggests that it appeals to something quite primal in human nature.