As a term, it's called 'paddywhackery' and it was, or indeed still is, a common cultural trope designed to deride the Irish as drunken, violent, stupid or immoral, or indeed a combination of all of these. As a cultural tradition, it has a long and storied legacy; some of the earliest non-native accounts of the Irish people come from Gerald of Wales' Topographia Hibernica and Expugnatio Hibernica, the 'Topography of' and 'Conquest of Ireland' respectively. These are written in the 1170s as polemics intended implicitly to justify the Cambro-Norman invasion of Ireland spearheaded largely by Gerald of Wales' own uncles and cousins.

The Papal Bull Laudabiliter had previously suggested in the 1150s that Henry II might consider invading Ireland to bring the Celtic Church back into line with Rome, but had largely been ignored at the time. The invasion of 1171 was instead largely a private affair, undertaken largely by the Cambro-Norman Marcher elite under the guise of supporting the deposed Diarmait mach Murchada, but was in reality mostly an aggressive land-grab. This, of course, would be unseemly, and so Gerald's work is an excoriating attack on the Irish to frame the invasion as a moral and righteous crusade to save the Irish from their own depravity. According to Gerald, the Irish are a 'vile people utterly without virtue', wallowing in their own sin and depravity; frequently drunk and licentious, given to frequent violence, sodomy and bestiality. This is a narrative that crops up in Gerald's other works; in his Descriptio Cambriae he takes time out of his history of Wales to point out that while the Welsh have had their flaws, they've never been as bad as the Irish, who are just awful.