Apparently sex acts that are implied are questionable, and since the lips are an outline rather than an actual part of the image it probably should remain questionable.
The whole rating system is broken and useless anyways IMO. For one, danbooru certainly isn't a children's website by any perspective, so there is no need to worry about the indecency. Then I guess some people want to filter past the sheer amount of hentai dropped on this site but then explicit only covers sex. Questionable is supposed to cover the rest of the suggestive and soft core stuff, but then people get in the whole "partial nudity is art and safe", and even the guidelines don't suggest having safe filter out erotic stuff like underwear and images where pantry shots are the primary focus. It seems to me that switching from pretty much serious art/comedy vs erotic/suggestive stuff would be more helpful. But oh well.
Edit: Yeah I was wrong. I just realized one of the bullet points on the guidelines mentioned that.
Questionable covers sexual acts but not pornography, which I assume means that there has to be at least two people present and participating to make the jump to "pornography". It is obvious the lips represent another person so I'll switch it to explicit.
The whole rating system is broken and useless anyways IMO. For one, danbooru certainly isn't a children's website by any perspective, so there is no need to worry about the indecency. Then I guess some people want to filter past the sheer amount of hentai dropped on this site but then explicit only covers sex. Questionable is supposed to cover the rest of the suggestive and soft core stuff, but then people get in the whole "partial nudity is art and safe", and even the guidelines don't suggest having safe filter out erotic stuff like underwear and images where pantry shots are the primary focus. It seems to me that switching from pretty much serious art/comedy vs erotic/suggestive stuff would be more helpful. But oh well.
I disagree and will switch this back to Questionable. I don't see another person in this image, I see a vague line that is over some girls nipple. There is no "Sex act" being shown here at all.