Here is my question to you: is there anyone who knows more about the subject than I do? The key to becoming irritatingly is mere repetition. And take their tone of voice, their cough--by all means, it's a game I say. If that doesn't fit you, then just be sure to 'forget' their name on a regular basis so you can torture it in the weirdest ways around.
Another good trick if they have any horror for material things is to tease them by wearing something of the type which sets their teeth on edge. And of course there's the famous "but why?" game asking out on anything honorary for which they've been standing up.
That’s right, what we're aiming for here is not depressing them for an entire afternoon but simply a little bit of good-natured ribbing.