“Irish Exit” is a term used when a person leaves a place without saying goodbye to the people they are with.
Irish Exit is to leaving without saying goodbye: as Slim is to a nickname for an overweight person.
Early versions of the term Irish Exit come from Irish Americans leaving social functions like Church, football games, and plays. When the functions let out people would congregate outside and chat with each person they knew and say goodbye before heading home. This usually added 30 minuets to an hour to the evening. When there was little or no time to do the customary goodbye, the family would leave through the side door. The side door move became known as the Irish Exit. The term has come to mean leaving a place without saying goodbye to those you are with or those you came with.
Joe-"Where is Timmy?"
Pat-"He pulled an Irish Exit about an hour ago!"