Fuct!

All at once, lol

Wisdom of crowds, when the average iq is only 100?

Political ineptitude, average stupidity, general ignorance, and overall foolishness

Psychological insanity, psychosis, delusion, and disordered thought

Nuclear annihilation, atomic holocaust (blast, radiation, winter)

Pandemic apocalypse, bio warfare

Earthquake and tsunami devastation

Cataclysmic asteroid impact

Criminality explosion

Robot, AI, Internet sentience, self-awareness, and true intelligence

Volcanic ash cloud eruption

Economic collapse, global depression

Climate crisis tipping point

Environmental destruction, ecological/ecosystem…

  deforestion, desertification, fisheries, coral bleaching
  global, widespread, (sixth) extinction event
Hurricane, drought, flood, famine
burst dams, airplane crashes, grid blackout, solar storm

Alien Invasion!!

I don't think zombies are actually technically possible, but they make for fun movies.