Jennifer Van Grove, over at CNET:
The application, though eyebrow-raising in name, isn't as offensive as it would seem -- unless the word bang bothers you. BWF is essentially a matching service that connects two Facebook friends who indicate that they are "Down to Bang" each other.
It isn't immediately clear why Apple decided to remove Bang with Friends from the App Store. There are a few App Store app guidelines that might conceivably have been violated by Bang with Friends.
Objectionable Content: There are a couple of guidelines related to rejecting apps that are excessively objectionable or whose primary purpose is to upset users, but these don't seem to necessarily fit the bill. Bang with Friends surely couldn't be more offensive than some of the other 'hook up' apps.
Pornography: There are some guidelines regarding erotica or user content that is often pornographic, but as far as I know Bang with Friends (despite its crude name) doesn't actually involve this type of material.
Legal Requirements: There is a guideline that refers to rejecting apps that encourage reckless behavior, but that also does not seem to fit. Sexual promiscuity may not necessarily be advisable, but surely does not fit the requirements necessary to be regarded as 'reckless'.
After further review, it is still unclear as to why Apple decided to remove Bang with Friends from the App Store. Apple has recently been cracking down on apps for various reasons (many of them good reasons), but as many developers can attest to, Apple's review process can be mercurial, to say the least.
Source: http://news.cnet.com/8301-1023_3-57585116-93/apple-removes-bang-with-friends-from-app-store/