Too much coffee can induce aggression and paranoia

"People who drink too much coffee are at risk of caffeine psychosis, according to a new report. It found that too much caffeine can lead to marked changes in personality and make drinkers more aggressive, anxious and temperamental.

'Caffeinism' puts sufferers at further risk of anxiety neurosis, irregular heart beats, insomnia, muscle twitches, and nervous irritability."

I haven't noticed any aggressive, anxious or temperamental people around Starbucks. One thing I noticed though is how most, if not all, the people kind of stop at the same time and stare at the new person coming in.