An angry mob is a group of people ("mob") and protest, either violently or non-violently, against a common theme, object, policy or ruler which the "mob" finds offensive. Such "mobs" can take many forms, such as picketing, rioting and silent vigils.
Angry mob Wikipedia
The description of a member of an angry mob, or an angry mob in general, is generally negative, focusing on such aspects as their filth or ugliness. This can sometimes be done to undermine their beliefs/goals through an ad hominem.
The Roman pleb uprising (triggered by the economic crisis, threats from opposing nations, and massive debt) caused what has been described as an angry mob.
Various Occupy Movement groups have been described by various authorities as being "angry mobs". This labeling has also been criticized.