No response or smile is my suggestion.

Some posters with their response seem to be making the assumption that the occupants of the car were not whacked out on drugs, and not going to pull a pistol, ball bat, tire irons, shotgun - and put you in the hospital seriously or kill you, or attempt to do so.

And/or otherwise making an assumption that these are rational individuals and not total scum of the earth.

That could be a fatal assumption.