Not a thing. If you judge someone based entirely on their sex; it's just plain old sexism.
Sometimes used to suggest that sexism can only go one way (say, males can only be sexist against females) and that if a male experiences sexism it's not really sexism; it's reverse sexism. Or the opposite of sexism.
This is designed to downplay or justify the sexism the male is experiencing.
As a term, reverse sexism is as realistic as reverse theft. A Klan member may suggest that if a white person steals from a black person it's reverse theft.
I understand that you are being denied access to the domestic violence shelter because you're a man, but that's NOT sexism; it's only reverse sexism.