First known usage at Earlham College, Richmond, IN in the middle 1990's; slang tang refers to the state of being so incredibly crunk, as to have reached, "the other level." The word is derived from Wayne Smith's "Under Mi Sleng Teng" which can be found, among other places on the Big Blunts - 12 Smokin' Reggae Hits compilation album.
Variants include chang clannged; doobklanged, shitklanged, etc...
In conversation, the length of the word is directly correlated with just how slangtanged you or someone else is or was.
Man, I was slangtanged last night.