Say, what?
I don't think you can make such a blanket statement. It depends on how an individual law is crafted in a specfic jurisdiction. It may be that you could mount an "equal protections' challenge to a spicific law that applied only to men, but to say that any oral sex ban would fail on this account shows a remarkable lack of imagination.
In fact to write a law that makes fellatio illegal for men and legal for women would take a bit of creative writing in the first place.
What jurisdiction do you believe has such a law?