Special Dialogue Grunts are Grunts who have special monologues and are placed in the Halo games as Easter Eggs. There are three of them in the Halo trilogy: the Thirsty Grunt at the end of the level The Maw in Halo: Combat Evolved; the Cowardly Grunt in the Halo 2 level Uprising; and the Final Grunt at the end of the level Halo in Halo 3. Special Dialogue Grunts will not attack you and will die like normal Grunts if you attack them.
Halo 5: Guardians contains several special dialogue grunts scattered through its campaign, such as Dimkee Hotay and the Singing Grunt.