"refuse from smelting," 1550s, from Middle Low German slagge (German Schlacke) "splinter flying off when metal is struck," related to Old High German slahan "to strike, slay" (see slay (v.)).
"denigrate," by 1971, from slag (n.) in a secondary sense of "worthless person" (1788). Related: Slagged; slagging.
: this lame ''slacker'' attitude a la Jeff Spicoli from Fast Times at Ridgemont High
An indolent and detached person; shirker; idler: The epitome of the slang-slinging, wise-cracking slacker (1898+)
[revived in the 1990s to describe a sort of cultural anomie]