This scene is only in the Godfather Saga, but when Fanucci is exhortating money from the opera owner (with Vito and Genco watching)...

In this scene, the opera owner makes excuses for not paying Fanucci. Fanucci then offers advice to the opera owner to boost sales - see Sicilian songs not Neopolitan songs and then (the funny part), Fanucci begins dancing and humming Sicilian songs.

Of course probably the funniest scene is the slumlord who comes back apologizing to Vito - scared and totally apologetic.