Shirty in fact arrived around the same time as the mid-19th-century American phrase "to keep one's shirt on". Presciently, the Daily News in 1899 observed that, for the French and Germans, "the whole duty of man includes the duty of getting `shirty' on the slightest provocation. Till they recognise that `shirtiness' itself is the real enemy of self-respect, they must infallibly go on boring holes in one another in this fatuous way."
AN INSPIRED teacher could encourage textual scholarship by asking for a list of the differences between the English and American editions of the latest Harry Potter. Pudding/dessert; wonky/crooked; yet crumpet stays, as does shirty. Such is modern youth that this has been italicised to show it is not a misprint.