In 7th grade I made up this gematria:
???? ??? ????=??? ???? (in Parshas Chukas). I based this on Rashi, who says there that “yosheiv hanegev” refers to Amalek.
I didn’t know at the time that you need a mesorah for gematria, but my rebbe liked it and told it to his rav (I don’t remember what the rav said about it, though).