Sportive Etiquette

Wikipedia, definitive source on everything*, has this to say:

All-caps style
The most common capitalization scheme seen with acronyms and initialisms is all-uppercase (all-caps), except for those few that have linguistically taken on an identity as regular words, with the acronymous etymology of the words fading into the background of common knowledge, such as has occurred with the words scuba, laser, and radar — these are known as anacronyms (a portmanteau with anachronism).

I think we've a way to go before mamils is acceptable, I guess current usage would be MAMILs. Regarding the assertion that

Modern style is to use upper and lower for acronyms that make a word.

I'm not sure what you mean by 'make a word', but if you mean that they can be pronounced in one mellifluous swoop instead of being spelt aloud (cf. KGB) then NATO would be a suggestion to the contrary.
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*I jest