As in "Wow, dude, nice haircut... not!!"

Used on the streets of SiliconBeach 10 years ago, before appearing on SaturdayNightLive.

Perhaps derived from SmallTalk?

	 :	(dude wow: haircut nice) not

I thought this was popularized by Bill and Ted...

I thought it was Wayne and Garth...

I think it's probably in the song "Valley Girl" by the Zappa family, from about 1982.

Sorry. Of the trailing interjections used in that erudite & illustrious poetry, the closest is "no way!"

http://www.nanuq.com/ashleigh/lyrics/v/valley_girl.html

TrailingNot is a lot older than you think. We used it a lot in middle school around 1984. My mother, a high school English teacher, reported an outbreak in her school a few years ago. While idly browsing through one of the textbooks she used, I discovered what I believe to be the primary transmission vector for this meme (and definitely the one that infected both my and my mother's schools):

Bernice Bobs Her Hair, a short story by F. Scott Fitzgerald, c. 1920: http://www.sc.edu/fitzgerald/bernice/ - search for "not!"

Mom wasn't thrilled to learn that English teachers are largely to blame for the persistence of the phenomenon. -- GeorgePaci

Much older. Minus the pause, it can be found in Shakespeare - one of the characters says to another, "I like it not." -- DanHankins

I don't thing that is a true precursor of the usage being discussed. The "..., not!" is usually applied in a sarcastic (and presumably an attempt at humour) manner, as a sort of "logical NOT" of the preceding sentence. The Shakespearian usage was, iirc, at the time not unusual in conversation either.

The "Shakespearean" usage is still common in Dutch and German.

However, it is not in English, for the most part. It does live on in certain common prose phrases, like "I think not!"

The modern usage is, "Sentence. Not."

There's a full stop (a period) between the two sentences, and the second segment is a fragment representing the first with the "not" before the main verb, thus negating the sentence.

On the streets, it was typically used after wildly & obviously bogus bragging. "I can program in Modula! Not."

For me (www.ckk.com) the classic prototype instance (i.e. not the "first" or "defining" instance, but the "prototype" as the robin might be a "prototypical bird" for many people, in George Lakoff's "Women, Fire and Dangerous Things") was when Madonna was on the bed with Wayne & Garth on SNL, and at the end she said "Call me!.......... NOT!".

You had the intense emotional excitement and reaction of Wayne & Garth, (Madonna says to call her!) and then the long pause while it built up, and finally the puncture/deflation with the final NOT.