"I think that is a very nasty word and have never, ever heard it applied to men."
Well, gay men use the term to apply to men.
Generally, the word "slut" simply means someone who is willing to have sex with only minimal or no inducements. It's sort of redundant when applied to a lot of men, some of whom would have sex with a knothole in a piece of wood.
That's why it's more often applied to women who are willing or eager to have casual sexual encounters.
Actually, I think there is still a huge double standard when it comes to women, men and sex.
Men who have sex with anything that moves are considered macho and women who have sex with these desperate men are sluts.