An adjustment of UMIAC, a valid word in Scrabble, which is a term in the Scrabble community for “U might initiate a challenge”, preying on the inexperience of new players hoping they say UMIAC isn’t a word.
UMIACFI is for the Urban Dictionary version of Scrabble, meaning “U might initiate a challenge, fucking idiot”.
“What? UMIACFI isn’t a word!”
“Yes it is, we’re playing Urban Dictionary Scrabble, remember? You lose your turn!”
“FUCK!”