Someonewith the in-ability to comprehand that of which normal people can; to be delayed, impeded or proceed slowly.
Johnny: "Yo man, that nig looks shezzey."
Robert: "Fo real? that niggah be trippin aight to mezzey."
(robert walks over to suspected retard)
Robert: "Jo dude, sarp?!"
Suspect: "Ma as fop awj fsa'd?"
Robert: "..."
Someone that is not right in the head, Very dopey or even someone that has been on drugs that have fucked up there mind.
Example of a mong:
ME: You know I saw your dog fucking your mother today.
MONG: OMFGz0r where I will kill that fucker
ME: Wow your a mong!
MONG: What?
ME: Exactly
When one gets fucked from the back whilst bent over giving the other male a blowjob felatio. A girl, (or boy depending) is bent over. Two males are on either side of this person. On one end, a male is fucking a girl in the vagina or ass, while she gives the male on the other side a blowjob. During all of this, they push the girls body back and forth so she has to expell no effort. So, its like a dirty threesome.
"Dude, me and Kyletotallymonged her the other night"
"The one with the drawn on eyebrows?"
"Yeah, wanna mong?"