In DoTA (Defense of the Ancients) for Warcraft 3: The Frozen throne, it is when players are "MIA" (missing in action) from their lanes, presumably to go and gank (kill) another lane... therefore, players will say "care mid" as a word of caution.
Care mid can also be used totally out of context to explain general severity. (See example 2)
Player 1 "bot and top mia, care mid"
Girl "Why didn't we hang out today?"
Boy "Because your boyfriend was all like 'care mid' last time we sexed."
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