The use of this is popular to describe the actions of geeky wannabe IT technicians and their lackeys, and has nothing to do with people with Down's Syndrome.
The noun is also used to describe someone who mongs frequently and is thus a mong.
2. (Monged)- A vegetive state of mind/being usually effective after consuming large quantities of alcohol, weed, lsd, ecstacy etc or combinations of.
2. Steve's well monged after we spiked his drink with acid, muhahahaha.