Nobody Special (1970)

Zeff Culkin is nobody special, a timid teenaged stockboy who might be easily forgotten, if he were ever noticed in the first place. His life-long curse of social invisibility becomes a life-saving skill when a disgruntled co-worker takes the store staff hostage... but overlooks Zeff. Using his remarkable powers of utter insignificance, Zeff baffles the bully to save the only girl that ever made him feel like somebody special.