Coo Coo Kacu is modernized for the old English Term Cuckold - which refers to a mans wife having carnal relations with another man while she is still married to him, the cuckold. Thus coco kachu - Mrs Robinson - as between Ann Bangkroft and Dustin Hoffman in the movie The Graduate
Refer to Chaucer's Canterbury Tales, The Graduat Movie with Dustin Homan - Song lyrics to the Graduate include the term Coo Coo Kachu. Maybe I am just too old but what I remember is that in the movie The Graduate, Mrs Robinson, the person the song was about was taunted with koo koo kachu Mrs Robinson referring clearly to the fact that Mr. Robinson was a cuckold. This term coming from old English and meaning that the cuckold's wife, Mrs. Robinston, was screwing another man while she was still married.
I was in college when The Graduate came out and this was discussed for at least two full class sessions. We were also dicussing Chaucers Canterbury Tales at the time where one of the main characters was also cuckold.