you were in the backseat of Steve Car. Billy was there to even if he doesn't like it he did not liked it because he hates Steve because he hangs around kids that are 3 or more years younger then himself, but did it for you.

you were tracking a Demogorgon with Steve for the Secret project of Hopper. And it went through a portal-like thing that led to the Upside down. Billy knew nothing about the project, Demogorgon or the upside down

Billy: what the fuck are you doing, Steve!

Steve: Speeding up, to go through the portal.

Billy: are you fucking dumb, we will never make it.