Why does Billy laugh when Reggie is about to shoot him?
Is it because Billy didn't think that Reggie was actually going to do it? I mean, Reggie's hand is shaking when he's pointing the gun at Billy. Or Billy is like Ganz, where he has this imaginary "cloak of invincibility", that convinces themselves that they are incapable of getting shot.
https://www.youtube.com/watch?v=-be9Cm4DwFw