Sidebanger = From the Side I'd Bang Her. Intraocualar Excitement and inducement triggered from gazing at an attractive female.
Scenario: Driving next to some girl in a her car.
Shloimy: Yo Yo Homies , I'd bang her
Me: Fo Real??
Shloimy: Fa Real Homie. Dat is da shit....
Meanwhile we speed up in the left lane and get ahead of the car.
Me: Yoooooooo, she's madddd old. She's old enough to be your grandma's grandma. That's some sick shit bro.
Shloimy: Homie dat be sidebanger.
Me: Bro dat's still some sick shit. I wouldn't bang her at all from the front or the side. U be trippin.
long hair going down the side of your face
she wore her sidebangs over her one eye so long, she sees funny now.
Moving one's head back and forth to one side: A variant of headbanging
In an act of utter randomness, Joe decided to sidebang to the KISS video rather than boring ol' headbanging.