Those who use the term "meece off" are usually the meeces themselves. They like to call other people meeces because they think its cool or they think it might insult the other person (even tho they dont know what it means). This word doesnt really have a meaning.
if you add 3s to your meece it makes u more elite.
Quote wikipedia:
The plural of moose is "moose" not "meece" as it is often used jokingly due to the fact that the plural of "goose" is "geese.