While, perhaps, seductive kisses are skirting the line (more so if they're gifs or actual people I would think) as to what can actually be posted directly in the thread using image tags, it's really up to personal discretion as to what is 'too NSFW' to post in directly in the thread. A rather brief overview of what I understand the rules regarding potentially NSFW content would probably be something like:
Ok to post:
-Hot guys wearing clothes.
-Face pictures of men.
-Help regarding potential preparation for sexual activities that are not graphic (i.e. "buy lube", "use condoms", etc.).
Less ok but still allowed unless it oversaturates the thread, if in doubt simply link the image under which circumstances they should be fine:
-Topless pictures of men.
-People partaking in a quick kiss (that is, not eating the face off of one another; these shouldn't be posted in large quantities).
-Personal stories of a sexual nature spoiler tagged that do not delve into graphic detail.
Not advised at all, a direct link is probably the absolute most that should be done and, even then, your own discretion should be used with regard to how risky it is:
-Men only in underwear.
-Suggestive pictures.
-Pictures of bulges (in underwear of course).
-Very intimate kissing.
-Links to the above that are not clearly and explicitly labelled as NSFW (with details of what's contained inside).
-Detailed erotic stories spoiler tagged (even still, this is really pushing it; if you're writing an erotica this thread is not really the best place for it).
Never allowed, ever, don't even link them:
-Nudes.
-Pornography.
-Pictures/Gifs of intimate sexual content that's beyond kissing.
-Websites that contain any sexual content.
-Extremely sexually suggestive content (i.e. a gif of somebody [pornstar?] masturbating where his penis cannot be seen, but it's clear what he's doing; a bad example probably, but hopefully it's clear what I mean).
-Links to Tumblr's with any pornographic content (this is covered by "websites that..." but it needs to be repeated as it happened in the last thread).
-Artwork of an explicitly sexual nature.
The exception to this is that, if the content is clearly for an educational purpose only, it can be possible to post (such as if the thread were to begin discussing STDs, it would be justifiable to link to a Wikipedia page on gonorrhea providing it's correctly labelled and the NSFW content is noted; I'm not trying to suggest that if somebody asks how to perform oral that you can go posting a link to some pornography featuring a blowjob), but generally it's just a case-by-case basis and if the individual has any doubt as to how suitable it is to embed in the thread it should be linked with a "NSFW" tag, and if there's any doubt about whether it can be linked it shouldn't be just in case.
EDIT: Oh and obviously a big thing that should probably noted is that you shouldn't flood the thread with potentially/definitely NSFW content as otherwise it could be locked which would certainly be a disappointment for the LGBT+ community on NeoGAF.
Mumei can likely chime in on the topic better than I can for obvious reasons, but that's my general perception of the guidelines for posting potentially NSFW content.
