Too Much Caffeine!
Unfortunately the streets of New York City have become a haven for unfortunate, mentally disturbed people who have been left to fen for themselves. Virtually every other corner has a poor soul who should be institutionalized instead of begging for spare change while swathed in filthy clothes and basically shunned by every passerby.
However, in the video you are about to view is that rare occasion when the person who is acting completely irrational and psychotic appears to be perfectly normal. Which can be the only possible reason why this dude sat across from him for so long before all hell broke loose.