miffed
日本でも年賀状の遅配というのがありますが、こちらは規模が違うようです。
miffedは口語で「少し怒って、ムッとして」という意味で、"slightly annoyed or upset"(LDOCE)です。slightlyがポイント。(UG)
UPS Overload Leaves Miffed Customers Short of Presents, Meals
If your gifts didn’t arrive on time to place under the tree this year, United Parcel Service might be to blame. The nation’s largest package carrier failed to deliver all packages to consumers by Christmas Eve, deflating the holiday spirit for some irate customers.
In a statement, UPS said it simply could not keep up with last-minute shipments as “the volume of air packages in our system exceeded the capacity of our network.”