A friend and his wife were watching t.v. The wife uttered this, discussing someone who believed what they heard. It is a congruent conflation of “drinking the Kool Aid” and “buy into it”, both meaning to go along or believe in an idea because of peer pressure. The former expression derives from the November 1978 Jonestown deaths, in which over 900 members of the Peoples Temple, who were followers of Jim Jones, died, many of whom committed suicide by drinking a mixture of a powdered soft-drink flavoring agent laced with cyanide and prescription drugs Valium, Phenergan, and chloral hydrate, while the rest of the members, including 89 infants and elderly, were killed by forced ingestion of the poison. A big thanks to Martin Pietrucha for hearing this one and passing it on!