The Great Q-section
Chengcrates had to think about this question for a while.
STOOGE vs. NINNY
Both of these obviously imply negative actions/attributes. A good thing to start off with is answering why Fat is a Ninny. He is a ninny by name, but he also fits the definition of ninny. How does this differ from a stooge. We'll take Fudgemaster as our example of a stooge. Instead of the action being from an uncontrollable source (fat's ninny brain), the person still manages to churn out "ninnish" actions. This calls for an example, since these words are intertwined no matter how you look at it in Chenglish. We'll say Fat and Fudge both fail in trying to cross a river (the negative action). Fat (doesn't have his canoe), the ninny, would have a thinking fault. This means that he would build a raft with more logs on one side or something like that and pull a tipper gore. "Ninny" would be the response from the peanut gallery. Fudge, the stooge, on the other hand would build a perfect raft, probably even complete with a seat and cushion. The stooge would then proceed to mis-balance his own weight on the stoogecraft, and would fall into the river. "STOOGE" would be the response here. This means that he failed in his action of crossing. I believe this proves the main difference between a stooge and a ninny. A ninny naturally fails due to himself, without control on the situation. A stooge fails in his execution of an "unninnified" or a "should work" idea. This difference has led stooge to be used more when talking about actions and ninny to be used more in pre-action ways. Please add something to this, as this distinction causes mass confusion without clearup involved.