That's why a passenger should always be holding on and why I always let the chick know before I accelerate hard. All it takes is for you to grab her arm and pull it around you so she knows. Wouldn't ever want a chick to get hurt due to me.
Partially the guys fault you can see him going wot like an idiot (the bikes are stacked , was he really going to impress somebody doing that ? ) and then she slides back . So lucky she had that backpack on .