Aggressive body language

A significant cluster of body movements is used to signal aggression.
This is actually quite useful as it is seldom a good idea to get into a fight, even for powerful people. Fighting can hurt you, even though you are pretty certain you will win. In addition, with adults, fighting is often socially unacceptable and aggression through words and body language is all that may ever happen.
Threat
Facial signals
Much aggression can be shown in the face, from disapproving frowns and pursed lips to sneers and full snarls. The eyes can be used to stare and hold the gaze for long period. They may also squint, preventing the other person seeing where you are looking.
Attack signals
When somebody is about to attack, they give visual signal such as clenching of fists ready to strike and lowering and spreading of the body for stability. They are also likely to give anger signs such as redness of the face.
Exposing oneself
Exposing oneself to attack is also a form of aggression. It is saying 'Go on - I dare you. I will still win.' It can include not looking at the other person, crotch displays, relaxing the body, turning away and so on.
Invasion
Invading the space of the other person in some way is an act of aggression that is equivalent to one country invading another.
False friendship
Invasion is often done under the cloak of of familiarity, where you act as if you are being friendly and move into a space reserved for friends, but without being invited. This gives the other person a dilemma of whether to repel a 'friendly' advance or to accept dominance of the other.
Approach
When you go inside the comfort zone of others without permission, you are effectively invading their territory. The close you get, the greater your ability to have 'first strike', from which an opponent may not recover.
Touching
Touching the person is another form of invasion. Even touching social touch zones such as arm and back can be aggressive.
Gestures
Insulting gestures
There are many, many gestures that have the primary intent of insulting the other person and hence inciting them to anger and a perhaps unwise battle. Single and double fingers pointed up, arm thrusts, chin tilts and so on are used, although many of these do vary across cultures (which can make for hazardous accidental movements when you are overseas).
Many gestures are sexual in nature, indicating that the other person should go away and fornicate, that you (or someone else) are having sex with their partner, and so on.
Mock attacks
Gestures may include symbolic action that mimics actual attacks, including waving fingers (the beating baton), shaking fists, head-butts, leg-swinging and so on. This is saying 'Here is what I will do to you!'
Physical items may be used as substitutes, for example banging of tables and doors or throwing . Again, this is saying 'This could be you!'
Sudden movements
All of these gestures may be done suddenly, signaling your level of aggression and testing the other person's reactions.
Large gestures
The size of gestures may also be used to signal levels of aggression, from simple finger movements to whole arm sweeps, sometimes even with exaggerated movements of the entire body.

Source: http://changingminds.org/techniques/body/aggressive_body.htm