Dirtie Gertie means: Dirty is an item in the gertie. The gertie can be pants or any other type of clothing that covers the legs. Depending on who is wearing it, the dirtie may be large or small. You might also find a dirtie gertie if you are gay or have the name David. Don’t be rude to dirtie gerties, as they are small and fragile, and will eventually hurt you in ways that your gertie can not explain. (in Community Dictionary, added by Ascensión Vidal)