I personally think Teatime was protesting too much. I think Terry Pratchett was echoing an old joke, like the one I heard about from Young Frankenstein, where the titular character and Igor protest the pronunciations of their names. There's a similar running gag in the Youtube series Helluva Boss, where the main character, Blitzo, insists that the 'O' is silent. For added points, he's also an assassin.
Also, on a mostly-unrelated note, 'Theodore' means 'God's gift'. Which explains any egotistical Theodore...