Green’s Dictionary of Slang

(US campus) someone who clings to the styles of the 1960s; an environmentalist.

1996

Eble Sl. and Sociability 63: In the eighties and nineties people who clung to the styles of the earlier decade were described with gentle disparagement by things associated with the back-to-earth movement, for example, earth muffins, ferns, granolas, grape-nuts, groovers, and hey-wows.