Spanish slang, literal translation: The Boss of Bosses. Actual usage is intended to infer something or someone is the very best, often with braggadocio.
"Yo soy el mero mero"; I am the top dog, the best.
"Oy abuelita! These pancakes are el mero mero!"
"Our canned menudo is el mero mero!"
"Oy abuelita! These pancakes are el mero mero!"
"Our canned menudo is el mero mero!"
by Akimbojoe December 31, 2017