That’s a good indicator for whether something should be marked NSFW or not. If showing the image to someone could be considered workplace harassment, you should probably mark it NSFW. The lines are pretty blurred, but it’s just marking a post so it’s better to air in the side of caution.
On Reddit, there used to be r/19684 for a non-horny 196 so it mattered less because the people that didn’t like the horniness had a separate space. I’m down for a good hornypost, but I also recognize that we’re now sharing a space with people who made an entire different subreddit to avoid the hornyposting. Especially with how touchy or painful sex as a topic can be to some people, I think it’s just important to be cognisant of our posting on a platform with no algorithm where every one of our posts are initially equal in visibility.