A
belittling expression describing a person who has
succumbed to
propaganda or
brainwashing. The reference arises from the
Jim Jones Jonestown incident, in which a
deranged cult leader convinced a large group of his followers to poison their children and then kill themselves, all using
cyanide-laced
Kool-Aid as the agent (well, actually it was a Kool-Aid lookalike, but what can you do).
Example: "I used to be able to talk to him, but then he got a job at Microsoft and drank the Kool-Aid; now he runs around yapping about how C# is going to take over the world."