A number of derogatory terms incorporating stereotypes about the Irish began to emerge, including “Irish confetti” for thrown bricks and “Irish kiss” for a slap. Irish twins fits into this vernacular, and is actually insulting on multiple levels.
Firstly, the term pokes fun at the stereotypical fertility of Irish Catholic families, which traditionally do not use birth control. In addition, it implies that the Irish lack the ability to plan ahead or control themselves, having children in quick succession rather than responsibly spacing them. Finally, it suggests that the Irish do not understand the medical definition of twins, which involves two children conceived and born together.