There's also the reverse: what boy songs could be transformed if sung by a female? The obvious actual example of this is Aretha Franklin singing Otis Redding's "Respect."
In Redding's reading, a brawny march powered by Booker T. and the MG's and the Memphis Horns, he called for equal favor with volcanic force. Franklin wasn't asking for anything. She sang from higher ground: a woman calling an end to the exhaustion and sacrifice of a raw deal with scorching sexual authority. In short, if you want some, you will earn it.The trouble with a man singing that song is that it's a bit ugly: I make the money, so you owe me. It's the conventional arrangement. The lyrics are a bit awkward in the female re-sing. Why was Aretha giving this guy "all my money"? But we ignored that. It was the remnant of the Otis version. She sang through that and pulled out the better, female meaning through sheer force.
"For Otis, respect had the traditional connotation, the more abstract meaning of esteem," Franklin's producer, Jerry Wexler, said in his autobiography, Rhythm and the Blues: A Life in American Music. "The fervor in Aretha's voice demanded that respect; and more respect also involved sexual attention of the highest order."
UPDATE: The classic example of a man singing a woman's song is Frank Sinatra singing Gershwin's "Someone to Watch Over Me." He's forced to sacrifice the most beautiful couplet -- "Although he may not be the man some/girls think of as handsome" -- but singing words that are an entirely conventional woman's dream, Sinatra lets us see a shocking, haunting vulnerability.