It's merely a common term that fits a wide spectrum of potential concerns. (Naturally, anyone on the internet is already in a place that isn't necessarily "safe for work", nsfw, nsfl, nsfh, &c flair is nonetheless helpful for those trying their best not to accidentally select a repulsive image, such as a public sculpture of Trump, which promped the request for an NSFW flair on a comment that could not be applied; hence the present request.)