Two meanings:
(a) A man who is
comfortable with or embraces typical working-class dress, usually work clothes, that have changed very little over the years.
(b) A man, usually a
young man, who enjoys
dressing up but in the outmoded 'square' fashions of the Fifties and early Sixties.
.
(a) Tom dresses
like a bear but he's not gay. In that flannel shirt, work jeans and lace-up boots, he's classically retrosexual.
(b) Jeff loves to scout out fedoras, slim ties and Ivy-League cut suits. The more he looks like
Frank Sinatra in the late Fifties or a character from TV's MAD MEN
in the early Sixties, he is really pushing the retrosexual button.
.