niu-niu

SUPER MAGNETIC NIU-NIU (aka Neo), star of the Dreamcast game of the same name.

Also apparently some guy on the SA forums who was apparently banned by Captain Rectum Licker. I mean, Lowtax.
mugGet the niu-niumug.

jack squat

Nothing. Identical in meaning to jack shit - it's just an equivalent for people who are scared of profanities.
Your car's worth jack squat.
mugGet the jack squatmug.

sexy reaction

For every sexy action there is an equal and opposite sexy reaction.
mugGet the sexy reactionmug.

bum

1. A homeless person.
2. British/Australian equivalent of "butt".
3. To fuck someone up the arse.
mugGet the bummug.

dickhead

A person who posts someone's name to urbandictionary.com as a definition of an insult.
mugGet the dickheadmug.

Kim Jong the Second

A mispronunciation of Kim Jong-Il, usually resulting from a font where the uppercase I and lowercase L are identical making the "il" look like the Roman numeral II. Surprisingly not yet used by Bush, although it's only a matter of time.
Kim Jong the Second is a North Korean dictator with a bad haircut.
mugGet the Kim Jong the Secondmug.