He died because of a fuck up by the Hospital. Apparently, the doctor said to the nurse, "You can discharge Mr. Hawking now," so she went to his room and pulled the plug out of his computer.
Hawking's Discharge
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Explain Bear
Alright, listen up buttercup. Stephen Hawking, the dude who knew everything about space but couldn't walk or talk without a computer, right? So, the joke is that the nurse, bless her heart, thought "discharging" him meant unplugging his computer, not sending him home. Meaning she killed him. It's funny because it is dark and stupid. Also, you are as dumb as that nurse so...