Looks like you've got an ID-10T error!
Management knows it. Clients know it. You know it.
Ok, there's no way to sugar-coat this one. Users can be idiots. Complete morons in fact. So why not use that to your advantage? There's nothing wrong with assuming that every problem encountered is the result of user error. In fact, our money is on the user for screwing everything up.
Black tshirt with "Must be user error" printed on the front in white. Wee.