It featured a man with erect genitals and a female child positioned over them, as if ready for insertion. You didn't see the child's genitals (obscured by a skirt).

And yes, vintage_sex is about porn pics, but I think content like that goes beyond what is generally accepted to be mainstream porn. I didn't mind the fact the link was posted, just that there was no warning of squickableness. People use terms like "hardcore", "NSFW" and "male sex" when doing other posts to that comm, and that gave me the impression that the comm was fairly mainstream in its notions of acceptability. I'm not one to do a major flounce over something like this, but I am going to be somewhat more wary from now on in.