Drink the Kool Aid is an expression, referring to the Jonestown mass suicides of 1978, led by Jim Jones.
The phrase carries the meaning of believing in an idea or concept with too great fervor, risking one’s own life.
The expression arose following the events of 1978, when over 900 members of the Peoples Temple movement died, which is referred to today as the Jonestown Massacre.
At the event, people drank a drink, called Flavor Aid mixed with potassium cyanide, causing their deaths.
This Flavor Aid substance would later be referred to by Americans as Kool Aid, due to it being more familiar to US citizens.
“Drink the Kool Aid” had turned into a colloquial expression over the years, reminding people to take everything they hear or read with a grain of salt.
The phrase was first written about on Urban Dictionary in 2005.