In Game Grumps' playthrough of Sonic '06 , episode 88 entitled, "Love Interests," Jon coined the term "grut" as a shortened form of "grump rut." The duo were initially discussing the notoriously overall bad design of Sonic '06, in which they have often stated in their playtrough, when Jon claimed, "We've gotten into a grumps rut. A grut, if you will."
The definition of grut, in Arin's point of view, is the excrement of a dolphin after the dolphin has jizzed (ejaculated) and bled.
For example, "Gross, is that grut?"
In Jon's perspective, grut "sounds like a really good one-night stand."
However, the definition could also be known as the infamous "grump rut," in which Jon and Arin are in a metaphorical "rut" in their ramblings; when their conversation begins to become repetitative and lacking unique content.