I was watching a funny video just now that was clearly not "Family Friendly" on a site I'd never visited before and noticed they were running AdSense ads. I checked out a few other pages until I found what I was looking for...another NSFW Video that was labeled as such by the site. On this page the space where the ads should have been was blank (AdSense code was still in page source). The first page was displaying ads because it didn't have any words (use your imagination)that would trigger the ads not being shown.
So, apparently Google has filters in place to detect NSFW or not Family Friendly content and then doesn't display ads. I would think a site like this would eventually get flagged and banned once a human actually looks at the pages that have been flagged...or does Google just look the other way?