I guess this is an example of what SuperCreeper1000 was refering to
(just girls in bikinis...but context and presentation probably makes it NSFW).
The screenshot above likely wont help you much, all you get is what I guess is your own adfoc.us ID and nothing that identifies the specific ad but it serves as an example.
I got this one when downloading latest Forge Universal for 1.9.4.
My guess is that the proper way to complain about ads like this is to complain directly to adfoc.us as I doubt you (as an adfoc.us user) can do much about specific ads but I got distracted from that after clicking the "report ad" link where they asked me to specify how this ad violated their ToS for ads because I wasn't able to find a ToS directed to the ads themselves, only ToC/ToS directed towards the users of the service (ie you guys).
The text in the actual ad is in Swedish, badly machine translated Swedish but even so.
It claims they have 1000s of horny members who for some reason wants to come and hang out with or at least near you and also some sexy women, who happens to be looking for f**kbuddies, that are apparently considering to remove one of their breasts but want your help to decide which one via a poll that is asking something that sounds kind of like "Which breast should they have?"...I'd be inklined to answer "both" but I guess I'm a bit weird like that.
Thinking about it, if the ad is inappropriate then this post is inappropriate by proxy which makes me a bit conflicted about the whole thing but
a: it was already posted on/via this site by adfoc.us and
b: you asked for it and
c: it's not THAT bad (relative Internet standards), it's just not something you'd expect to find anywhere near "Family friendly".
If this IS crossing the line and the post is edited/deleted, please don't kill the messenger in the process (I'm usually very well behaved) :-)