this is actually a genuine question!!! Where did he come up with the idea to stutter during that particular song? Or is he pretending to be on coke or something? Or was he actually ON coke during the recording session?
Mr Daltrey is mimicing the amphetamine-fuelled speech of the sixties Mods. The 'blues' gave them extra energey, but made them so hyper that their brains ran ahead of their mouths, causing a frequent stutter when speaking. It's that which is aluded to in the song - separating youth from the older generation with a knowing reference.