I’ve heard the expression “someone’s been drinking/drank the cool aid” multiple times. I know coolaid is a drink or something but it doesn’t really make sense in the context. I feel like there’s some type of cultural reference here. Could someone explain what this means?
"Drinking the Kool-Aid" refers to the mass suicide of the "People's Temple" cult at Jonestown, Guyana in 1979. Hundreds of members of the cult are incorrectly believed to have killed themselves by drinking fruit-flavored punch laced with cyanide. Actually, the drink believed to be used was the brand Flavor Aid, NOT the brand Kool-Aid, but "drinking the Kool-Aid" became a saying that means slavish adherence to a delusional belief. This despite the fact that cult members were murdered after trying to escape, rather than slavish adherents. See the 4th Wikipedia paragraph for details.
Sara T's explanation is often thought of as the origin, but the expression actually started getting used by "baby boomers" after Tom Wolfe's The Electric Kool-Aid Acid Test came out in 1968. The book chronicles the activities of Ken Kesey, one of the leaders of the hippie counterculture movement, and his followers, in particular their habit of getting together and taking LSD in order to have some sort of revelatory experience. (Electric Kool-Aid is Kool-Aid laced with LSD, and was popular at parties back in the day.)
From the linked article about the book:
The Acid Tests are parties where everyone takes LSD (which was often put into the Kool-Aid they served) and abandon the realities of the mundane world in search of a state of "intersubjectivity."
"Intersubjectivity" is achieved by subordinating one's subjective understanding of reality to a group-defined consensus of reality revealed by the "enhanced insight" that one derives from being high on LSD. (In the case of the book, it would seem that that "consensus reality" is pretty much what Ken Kesey says it is.)
The book was very popular in the hippie counterculture of the time, and people who were "into" that counterculture (including me, at least to some extent) were often said to have "drunk the Kool-Aid."
The definition got broader as time progressed, morphing into the more general meaning of "slavish adherence to a delusional belief" that Sarah describes, and given a push in that direction by the horrific event at Jonestown, and the similar Heaven's Gate incident.
(I sat around talking with some of the latter's recruiters for several hours over a couple of days when they visited my campus back in 1977, but I never drank the Kool-Aid.)