I think, when sending a picture to someone who has their NSFW settings to "No thanks" or "Not at first," the sender should get a Clippy style pop-up.

It could say something like "Keep it PG, folks! This user doesn't want to receive NSFW messages. Please check your message for inappropriate content." Or "Preserve the mystery! This user doesn't want NSFW pics right off the bat. Please check your message for inappropriate content."

Now, this would be annoying as all hell, but there are obviously a lot of guys who need the reminder. I understand that the occasional unsolicited dick pic is a hazard of dating apps, but it's making the app unusable.