If you are talking about the same ad as I think you are, which you may not be as different visitors in different countries get different ads, it is extremely far from a 'naked boob', while mildly sexually oriented, and a type of ad we try and prevent from appearing with our ad network (sometimes this is possible, sometimes it isn't), I wouldn't call it 18+ by any measure.
If you can take a screenshot of the ad and send it to Colin (barmyarmy), who deals with the advertising, he will try and get it taken off the site. But as ad campaigns are very dynamic, it's a catchup with trying to avoid them, we do make an effort to avoid them.