When I was still teaching, I would occasionally ask my students to
propose a male equivalent of "slut" -- i.e., a word that had all the
polemical force of "slut" but that clearly and unambiguously applied to
males only. No one ever came up with a really persuasive candidate. The
brighter women in the class would often fall back on "asshole,"
acknowledging that while it wasn't specific to males, it was the best
epithet that didn't focus on females. It is really amazing how much of
the available language of contempt is gendered, in origin and usually in
current usage. "Son of a bitch" is classic: aimed at men, but focusing
on their mother, as though the worst thing you can say about a man is
that he has a sexually erring mother.
Carrol
I've heard my students use the term slut for males as much a females. This is a change from when you were teaching. The word has the same meaning but cannot carry quite the same contempt since our culture praises sexually active males and not females. Sluts are no longer exclusively female.
I don't know when slut began being used as often for males.
In a related vein, The Richmond Sluts are all male. They are also an absolutely fantastic band. Way under- rated.
John Thornton