zero, adj. — Green’s Dictionary of Slang

zero adj.

useless, worthless.

1979

‘Iceberg Slim’ Airtight Willie and Me 38: You jive flat-backing zero bitch.

SE in slang uses

In compounds

zero cool (adj.) [cool adj. (3)/SE cool, i.e. ‘no heat whatsoever’]

(US campus) extremely aware, sophisticated.

1965		Time 1 Jan. 56: The ancient real cool is still admired [...] but the University of Florida has gone on to zero cool.
1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 46: zero cool – As cool as possible.

zero-hero (n.) [their alcohol consumption is zero]

(UK teen) the designated non-drinking driver escorting their drinking friends for a night out.

2001

OnLine Dict. of Playground Sl. 🌐 zero-hero adj. the ‘designated driver’. Someone who doesn’t drink alcohol at a social gathering etc so that those who do drink can drive home in safety.