He Was a Quiet Man (2007) on Netflix

Plot summary

At the ADD company in Los Angeles, Bob Maconel is the man nobody consults or invites anywhere. His neighbors pay him no attention, and at home he talks to a goldfish in his aquarium. Now and then he pictures himself shooting the people he works with or blowing up the building. One day a man in the next cubicle breaks down and fires at the staff. Bob shoots him and finds Venessa Parks, an executive he never had the nerve to approach, wounded on the floor; he gets her to safety. The city calls him a hero. His boss, Gene Shelby, promotes him and hands him Venessa's old position.