I'm probably with the party-poopers on this ... even though I'm very much in favor of creativity and usually against cultural narrowing.
After reading the Server Rules (again,) I feel that they indicate a stronggg emphasis on mutual respect and appropriateness, with ZERO tolerance for sexually explicit content or adult themes. SchoolRP has strict regulations regarding age-appropriate character relationships and actions. And calling someone a MILF is probably somewhere in there.
At least from reading the rules, I feel that the server is intended to be safe for younger players, and its overall appropriateness should somewhat align with the Minecraft ESRB rating of Everyone 10+. Which would suggest that the content we write/roleplay should be suitable for ages 10 and older: cartoon, fantasy or mild violence, mild language, and/or minimal suggestive themes. (Of course, ACTUALLY PLAYING on the SchoolRP server gives me a different vibe, but there is always a discrepancy between rules and execution.)
Rule 2.1 emphasizes respectfulness and disallows oppressive behavior including sexism, which could be construed to include derogatory or objectifying language.
Rule 2.7 prohibits inappropriate topics, specifically those of a sexual nature. If the term "MILF" is used in a sexual manner, it could likely be a violation of this rule.
Rule 4.3b implies that character names cannot be inappropriate, which might extend to the use of certain terms in character descriptions or dialogues.
Rule 5.3 outright bans erotic roleplay, along with detailed NSFW content, including 'erotic literature'.
So "MILF" could be interpreted as falling within the categories of sexism, inappropriate topics, or NSFW content, depending on the context of its use. My instinct tells the that it should be at least disencouraged, or even restricted, particularly if it is used in an inappropriate, offensive, or sexual manner.
In the end it's about overall player comfort. I'm looking forward to the poll suggestion.