A term used to describe people who are mentally retarded. It stands for Mildly Mentally Impaired. Also used as a different insult, instead of using the wordretarded.
Rachel: You are such an idiot.
Brian: Well, you're MMI.
Acronym for "made me incostruably laugh." Because the adverb "inconstruably" does not exist, it can properly reflect the degree to which something made you laugh when you are in an uncontrollable fit of laughter.