Green’s Dictionary of Slang

(US teen) good or cool.

1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 42: tuff – Fabulous and groovy; wrapped tight; you like it; good-looking and popular.
1988		Eble Campus Sl. Mar. 10: tuff – pretty, sexy; exclamation of elation: ‘We don’t have class tomorrow.’ ‘Tuff!’.