For the uninitiated, generally NSFW is for sexual contents and NSFL is for gory contents. People may want to see one but not see the other at any time for any reason. I have seen this feature requested over the years in Reddit but it never happens. Maybe now some instance can finally implement it?
"Duck tape" actually has a longer history than "duct tape." While there is also branded Duck™ tape, duck tape, as in adhesive cotton duck, has been around since the 1800s or so.