Again, not important. Do not care. It doesn't matter.
MMI is not the problem. It's just a symptom of a problem at the table. Typically it's a symptom of a disconnect somewhere between the players and the GM about how to resolve things at the table. For a table with
@tetrasodium and
@hawkeyefan, this would mean that the table is dysfunctional and someone at that table is unhappy. Who cares what the actual definition is? This ultra-pedantic need for nailing down a single definition is largely the reason why these conversations go round and round in circles because you will never, ever find a single definition of nearly anything in the English language that all people will agree about, let alone a made up bit of gaming slang.
Hmm. "[U.]ltra-pedantic need for nailing down a single definition" seems to be a weird thing to say when you're arguing so strongly for a definition that is singular in that it is bad.
Worrying about who is correct, who thinks it means this and who thinks it means that is completely and utterly missing the point. The point is, the table where someone is tossing out MMI as a criticism of play is an unhealthy table. Or, conversely, if someone says, "Hey, I play my game like this." and someone else replies, "Oh, I don't think I'd like that. Sounds too MMI to me", then those people should not play together.
I use MMI when I GM. I do not feel that my play is unhealthy. I'm keenly aware of the structure of authority, and that I, as GM, am responsible for gating player action declarations to align with my understanding of the fiction, and this keen awareness lets me run a better game because I can take active steps to mitigate problems that might arise from this structure of play. And to lean into it when it benefits play (and I think MMI can benefit play).
It's the endless search for "what's right" and "who's wrong" that turn these kinds of conversations into the total train wrecks that they become. It's the reason why dropping anything like Forge speak into a thread is just chumming the water. Or dropping a Tolkien reference as well. Off folks will go merrily trying to gainsay the other, meanwhile, all sorts of noise signifying nothing.
I don't really care about right and wrong, I mostly care about useful.
I do not care. I could not possibly care less about a "proper" definition of Mother May I. When used in context, nearly everyone knows exactly what it means and what it refers to. There really isn't any need to make a clearer definition. The reason it has come up "again and again" is because people absolutely refuse to accept the idea that some problems are self inflicted.
I argue that people know what it means as well -- it's a reference to a children's game where players have to ask the mother player for permission to do things. In 5e, the GM has the clear authority to determine how action declarations resolve. The effect of this is that players are essentially asking permission of the GM to allow what they want to transpire to be the outcome of their action declarations. There's a reason a lot of 5e play is players declaring actions to prompt the GM to give more detail so that the players can successfully align their actions and intended outcomes to align to what the GM is prepared to approve. And I don't think this is bad play at all -- sounds pretty much like how 5e is intended to play! It's how I run and structure my games, and is a good description of a lot of discussion about games you can find on the 5e forum, especially looking at asks for advice and the advice given for plotting, story, and resolving of actions in 5e. It's not bad at all -- it's the structure of the game, and MMI is a quick shorthand that shared enough similarity for someone to immediately grasp that this is what's happening. The problem, in my estimation, is really that people have a romanticized view of play that laying it out this barely is a shock and therefore rejected. I'm reminded of the opening to Love Song of J Alfred Prufrock, by TS Eliot --
Let us go then, you and I,
When the evening is spread out against the sky
Like a patient etherized upon a table;
The sudden brutality of the unexpected blunt analogy does the same work here as MMI does for 5e.
EDIT -- weird underline tag got applied. Figured it out.