I think it's the insinuation of "zero sperm count", which is a lot of guys excuse for BBFS.
But back to ass play and between all the theatrics, I believe the point of this post was when a lady says NO it means NO. Not try harder or keep asking. We also need to remember to be more straight forward and not grant these types of guys with any reason as to why we say NO. The minute you start giving them other responses like "I only do it with my boyfriend" or "I'll let you do it if I can do it to you", leads them to believe there's a chance. Just tell them NO and if they continue asking, block them. Simple as that. Don't entertain the BS or let it get your panties in a bunch.