Editor’s note: This column is an excerpt from Tom Purcell’s humorous memoir, “Misadventures of a 1970s Childhood,” that was previously distributed in 2020. Yahoo News reports that retro fashions from the ’60s, ’70s and ’80s have been making a comeback. That makes me grumpy. Because I’m still upset about the David Cassidy shag haircut my sisters made me get in 1973, when I was 11. As I explain …