I don't see it as sexist personally, but I can understand people taking issue with it from a graphic violence point of view. It's very graphic and blatant for a public picture that children are going to see. X-Men is not a children's movie, so if they're going to advertise it they could have at least done a non-violent shot.
"Adulthood is like looking both ways before you cross the road, and then getting hit by an airplane" - sarcasm_only
"Ironically like the nativist far-Right, which despises multiculturalism, but benefits from its ideas of difference to scapegoat the other and to promote its own white identity politics; these postmodernists, leftists, feminists and liberals also use multiculturalism, to side with the oppressor, by demanding respect and tolerance for oppression characterised as 'difference', no matter how intolerable." - Maryam Namazie
"Ironically like the nativist far-Right, which despises multiculturalism, but benefits from its ideas of difference to scapegoat the other and to promote its own white identity politics; these postmodernists, leftists, feminists and liberals also use multiculturalism, to side with the oppressor, by demanding respect and tolerance for oppression characterised as 'difference', no matter how intolerable." - Maryam Namazie