If you consider that the training set includes all western art from the last few centuries it’s not too surprising. There’s an awful lot of nudes in that set & most of them are female.
If you open up the script txt2img and img2img scripts, there is a content filter. If your prompt generated anything that gets detected as "inappropriate" the image is replaced with Rick Astley.
Removing the censor should be pretty straightforward, just comment out those lines.
It's kind of amazing that ML can now intelligently rick roll people.
I think it would be awesome to update the rickroll feature to the following:
Auto Re-run the img2img with some text prompt: "all of the people are now Rick Astley" with low strength so it can adjust the faces, but not change the nudity!!!1
EDIT: It was a false-positive (honest!) on the NSFW filter. To disable it, edit txt2img.py around line 325.
Comment this line out:
And replace it with: