In 1955, Boeing test pilot Tex Johnson, flying above Seattle's Lake Washington, rolled the Dash-80 (the precursor to the 707) and briefly flew the plane upside-down.
A 1:45-minute film of Williams recounting that flight is here, including a photo taken inside the plane when upside-down. (Don't fret, people who dislike flying: I won't embed it. It's your choice whether or not you want to see it!)
A slightly clearer 18-second clip is here.
A further description of people's reaction to seeing an upside-down plane is here.