Lead singer of the Jefferson Airplane.
IMO one of the hottest US singers of the '60s, along with Linda Ronstadt.
According to legend, the Airplane were doing an outdoor concert in NYC in the early '70s. Rain clouds were looming, and somebody onstage said the threatening storm would be averted if all the girls in the audience took off their tops. Grace obliged as well, and a photographer clicked:
I've seen at least one other bare-breast picture of Grace (she whips out a tit while drinking a can of beer) but I can't find it online.