Mike's first day at the bank in Psmith in the City:
'I've come,' was the best speech he could think of. It was not a good speech. It was too sinister. He felt that even as he said it. It was the sort of thing Mephistopheles would have said to Faust by way of opening conversation.
Psmith starts out his friendship with Mike by helping him steal a study. In order to actually explain why this is funny, I'd have to copy-paste the entire scene.
In order to get the attention of Baxter in Leave it to Psmith, Psmith simply picks up a flowerpot and chucks it through the window of his study.
Later in the book, Baxter tries to do the same thing to get Lord Emsworth's attention, leading to Emsworth thinking Baxter is insane and actually sending Psmith out to subdue him, armed with Freddie's golf club and wearing a carnation in the buttonhole of his pyjamas.
In Psmith, Journalist, when a threatening figure offers Windsor and Psmith a large sum to stop writing exposť articles, Psmith proceeds to give him a truly epic put-down containing the recurring phrase "Cosy Moments cannot be muzzled!"