I already mailed in a polite refusal. I'll still be in Canterlot, but I have other business to attend to at that time.

[There's a slight pause, and a skeptical eyeing of the mare on the other end of the scroll.]

While they did go a bit far in calling you "psychotic", remember that you're going to be going to Canterlot. To a formal event. I... don't know if you had the same upbringing as the Applejack from this Equestria did.