Sincerely Theodore is an episode of the Alvin and the Chipmunks series.
While Alvin practices for a play, he convinces Simon to make his bed and Theodore to respond to his fan mail. Theodore learns that Molly, one of Alvin's biggest fans, wants to meet Alvin. Theodore decides to go in Alvin's place as he's not interested. When none of his jackets fit, he goes on a diet with Simon's help. Alvin discovers that Theodore's date is the daughter of a famous film director leading him to insist on taking her out instead, breaking Theodore's heart. In order for Alvin to make it to his play and the date, Alvin gets Theodore to switch back and forth between the play and date. Simon assists, only for Theodore's sake. As a result, Theodore wraps up the play and is given a role in the director's new Broadway play.
- "Twist And Shout" originally performed by The Beatles.
- Alvin wears his cap when he takes a shower; he just places a shower cap over it.