"Say It Ain't So" is a song by Weezer which is about lead singer Rivers Cuomo's alcoholic step-dad, and how every time he drank, it pushed Rivers further away form him. Cuomo didn't drink until he was 21.
Cuomo's father began drinking when he was leaving Cuomo's mother. At 16, Cuomo discovered beer in his refrigerator and realized his stepfather was leaving his mother.
The video was shot at the garage in the Los Angeles where Cuomo and Weezer bass player Matt Sharp lived.