This finally explains the cutthroat people behind you in the Starbucks line: Psychologists have added caffeine withdrawal to their Bible, the Diagnostic and Statistical Manual of Mental Disorders:

[E]xcessive caffeine intake can cause a mental condition known as “caffeine intoxication.” People with this level of intoxication will show five or more of the following symptoms: restlessness, nervousness, excitement, insomnia, flushed face, diuresis, gastrointestinal disturbance, twitching, rambling thought or speech, tachycardia, arrhythmia, periods of inexhaustibly, or psychomotor agitation.

How that that cup 'o joe look right now?

Read more at Grist.