[Marty and Doc observe George's incompetence in 1955]
Dr. Emmett Brown: Which one's your pop?
Marty McFly: [points him out] That's him.
[they see him getting kicked around by other school bullies]
George McFly: [has a "kick me" sign on his back] Okay. Okay, you guys. Ah-ha-ha-ha. Very funny. You guys are being real mature.
Dr. Emmett Brown: Maybe you were adopted.