It would take a surprisingly small number of cups of coffee to kill the average human being.
By drinking it, that is. Not by some other way, like drowning in it. Hell, you could drown somebody in ten cups of coffee, probably, if you could keep them still enough while you hold them upside down and dunk their head in the bucket so they don’t tip it over with their inane struggling and spill the coffee everywhere.
Some people are so inconsiderate that way.
But that’s not what I mean. Specifics are in the following video, specifically at about the 2:55 mark.
Mania! Disorientation! Hallucinations!