'Back in 1963, everybody who knew anything about rock 'n' roll knew that the Kingsmen's "Louie Louie" concealed dirty words that could be unveiled only by playing the 45 rpm single at 33-1/3. This preposterous fable bore no scrutiny even at the time, but kids used to pretend it did, in order to panic parents, teachers, and other authority figures. Eventually those ultimate authoritarians, the FBI got involved, conducting a thirty-month investigation that led to "Louie"'s undying - indeed, unkillable - reputation as a dirty song.
'So "Louie Louie" leaped up the chart on the basis of a myth about its lyrics so contagious that it swept cross-country quicker than bad weather.'
[Dave Marsh, Louie Louie: The History And Mythology Of The World's Most Famous Rock & Roll Song]
'In retrospect, it's easy to identify the aspects of the Kingsmen's "Louie Louie" that made the "filthy lyrics" myth even a tiny bit plausible. The pidgin English narration of the lyrics was unusual enough, and comprehension difficulties were compounded on the Kingsmen's recording by several factors:
Lead singer Jack Ely had strained his voice participating in a marathon 90-minute "Louie Louie" jam the night before the session.
Ely was singing with braces on his teeth.
The boom microphone in the studio was fixed way too high for Ely, who had to stand on tiptoe and sing up into the mike.
What the band thought was a rehearsal run-through turned out to be the one and only take of the song.'
[snopes.com Urban Legend Reference Pages]