The NSFW isn't to be taken literally. In this case it''s a "I don't want to spontaneously see your weird ass bug and vampire kink bait when I didn't subscribe to anything that would reasonably have it, thanks". The tag gives viewers the ability to opt in.
What? No. Usually I don't answer or downvote criticism because not everyone has to like my/anyone's content and criticism can absolutely be valid. If you're serious though then I'd say sexualizing this image to that degree is quite a leap. I mean, the vampire is Sesame Street's The Count for starters. There's nothing sexually explicit or even implied in either the image or the text.
I would much rather have the NSFW tag be for what it says instead of a general "some people might not want to see this." I don't want to click something thinking it's the latter and get the former. A spoiler tag may be more appropriate if we have those.
Also, this is literally just a meme about bug bites and a vampire bite. The vampire in question being Count von Count from Sesame Street.