A recently-released study by the National Institute for Mental Health claims that five to seven percent of the population - perhaps up to 16 million Americans - suffers from Intermittent Explosive Disorder (IED), or what could be colloquially referred to as "road rage syndrome".

Symptoms of IED include multiple bouts of anger that are out of proportion to the situation and which include a threat of violence or actual aggressive action towards a person or property. Said to be related to improper functioning of serotonin in the brain, the average age of onset is 14, with an average of 43 outbursts over one's lifetime. For what it's worth, we suffered from at least that many violent episodes while changing the head gasket on a GM Quad 4, but we're pretty sure that could have been addressed by dropping the car off at a junkyard instead of visiting a psychiatrist.

[Source: Yahoo!]