The chest bump is a body language display used in a variety of different emotional settings. The example seen in this photograph shows a baseball player voicing his disapproval towards the referee. You can clearly see the intensity of his anger by how the ball player forcibly uses his index finger to illustrate his annoyance by thrusting it towards the ground. You can visually see how his anger manifests by the widening of his jaw, exposing his teeth, which alongside the chest bump, is classic primal human behavior we have adopted via evolution.
The chest bump behavior is not just seen in primates, as snakes often perform this display as seen in the picture above. The chest bump is used to show ones dominance over another; however the one who is physically ‘bigger’ than the other has a distinct advantage during this territorial ritual. Chest bumping is something that I like to call ‘social sparring’ where two people try to assert their physical prowess over each other without resorting to punching.
Chest bumping isn't exclusively used to intimidate, often it can be seen where jubilation is present. Basketball players in America often bump their chests after a highly skilled 3 point play, The Australian Beach Volleyball team use the bump after a victorious match, and even Barack Obama can be seen chest bumping every now and again.
The chest pump is not a behavior seen globally, especially in cultures where touching is frowned upon.
A very funny take on the positive side of chest bumping.