Dear guy idling his truck outside my office:

That truck is really obnoxiously loud. And I'm sure you know that, since you're sitting in it. You're also wasting gas.

Maybe you should think about someone besides yourself and turn the stinkin truck off, since you've sitting idling for at least 10-15 minutes? I doubt the restaurant patrons (who are closer than I am) are enjoying listening to it either.

Sincerely,
Back in the office and cranky.