the bag-over-the-face class
A crude and cheap form of combustible methedrine, favored by the same sort of addictive class that sniffs gasoline fumes or coats the inside of a paper bag with airplane glue and puts the bag over their face and breathes until they fall down and start to convulse.
Context
The bottom of the pharmacological ladder: a crude combustible methedrine for the same class that huffs gasoline and glue-bags themselves "until they fall down and start to convulse." The cheapest, most self-destroying end of the using economy, named without euphemism — the desperation-grade high.