WTF Moment: Dog in shop (pitbull in barber shop)

Here is a scary moment worth sharing that I found on youtube.  Imagine if you are at a store or (in this case) a barber shop and some aggressive dog comes in and starts biting and snapping at people?  This is exactly what happens in this video.  An aggressive pitbull somehow chases some dude into a barber shop and tries to bite everyone.  I hope everyone was okay in the video.  Not sure what would cause a dog to do something like that.  I suppose this is what can happen if people don't pay attention to their pets offleash.