Lead vocal: John
Larry Williams was another one of John's favorite artists. The Beatles recorded three of his songs; "Slow Down", "Bad Boy" and "Dizzy Miss Lizzy". Plus John included "Bony Maronie" on Rock 'N' Roll in 1975 and Paul also did "She Said Yeah" on Run Devil Run in 1999.
The Beatles' version is very faithful to Williams' original, although I think they drew out the intro a little longer than necessary. John pulls out that rockin' and screamin' vocal, although, I think by this time he's getting pretty tired of it (even though he would do it a few more times).
For technical geeks, there is a big goof on this, where John's second vocal flops the words during a verse. Although his vocal is double-tracked, they are two separately recorded vocals. It just goes to show that not everything George Martin produced and Norman Smith engineered could be perfect and that the Beatles were obviously in a rush to get this out (it was literally recorded two weeks before it was released).