I just went to Yakihonne while not logged in -- it took me to the Home "Global" feed. Scrolling down a bit to see what was there I was met with a link to "HD Porn Videos" and the preview image was essentially a frame from whatever video was being promoted.

I wasn't "blasted" with NSFW but it was definitely present (and not very far down the feed). And the feed seems to be chronologically ordered, so depending on your timing something like that could be front and center.