If you were to bump into someone and they get a little
aggressive make an apology -say you're sorry for bumping
into them. Say it firmly, but politely, so that they can feel
your confidence. If they pursue it place a fence between you
and them and back away. Tell them that you don't want
trouble. If they pursue it any further then you may have to
get physical, perhaps with posturing (later chapter) or even
an attack. If you do have to attack then make it pre-emptive.
Blocking and countering like they do in the films doesn't
work so don't bother trying.
An incident occurred recently when I was at the bar of a
private party where I had no other option open to me than to
stay. I went to the bar with Sharon and an ugly fellow stood
by the bar started staring at me. I tried to be polite because I
sensed that he wanted trouble.