A party or informal ritual at which a group of people take food and/or drink laced with LSD. The expression and the practise were originated by Ken Kesey and the Merry Pranksters, a group of hedonistic travellers in the USA in the early 1960s who were successors to the beats and precursors of the hippies. 'The Electric Kool-Aid Acid Test.' (Title of a book by Tom Wolfe, 1969)