Vine knows it when it sees it and chooses to ban porn

Porn: some people love it; some people are digusted by it, but we all know it when we see it, right? It's this 'we know it when we see it' approach that Vine is adopting with its new policy covering sexually explicit content on its social netowrk. Vine reckons that explicit sexual content isn't a 'good fit' for its community so its users will no longer be able to post looping six-and-half second videos of it. Vine doesn't, however, want to be seen as too prudish. Unlike Facebook and its draconian 'no nipples' policy, there's no banishment of bare breasts, and content showing nursing mothers, Femen protestors, and nude models will remain welcome on Vine. In fact, Vine estimates that in excess of 99% of its users won't be directly affected by the policy change. For anyone who violates it, however, the punishment is account suspension until the offending material is removed. Persistent posting of forbidden content will result in permanent account suspension. The changes are laid out in a blog post and a specific sexual content FAQ.

Vine maintains that it doesn't have anything against sexually explicit content, just that it would prefer not to be the source of it. Doubtless the App Store and its policies prefer that it wouldn't be the source of it, too.