Top definition
despite having a new girlfriend/boyfriend, sex with the ex is so good it must continue. Also known as Grandfathered in.
Guy 1: I cant go man I was up all night making sweet sweet love to Lisa.

Guy 2: Dude I thought you were seeing Veronica?

Guy 1: Lisa's a preexisting condition man! Shes Grandfathered in!!!
by ChiBlonde May 30, 2012
Happy St. Patties Day!