Since a lot of these replies veer into the not safe for life, gross, or sexual, I think I'm just gonna mention the mundanely "weird" few Hubzilla or Misskey instances I've stumbled around. It's less to do with their content and more with the different structure compared to some of the more common website styles you see outside of social media as well as distinct from much social media.
Like Hubzilla almost seems like a techie's idea of social media right down to the menus listing system apps and users' having file directories for, well, presumably sharing files? I've yet to find a Hubzilla instance with some more active use to see how it would all really pan out, but I have found at least one with some nicer looking css to it.
I think one of my favorite parts of looking through Hubzilla instances is that you can see this interesting potential for it as a cross between MySpace and like some power users' space for hosting odd web apps and files.
As to Misskey, well, many of the instances I've seen just have this really lighthearted vibe to them thanks to the design using a lot of round edges and...Something else with the visuals gives a lot of the instances a softer feel. Some of it's absolutely the custom emojis, but there's just a lot of weird playfulness to the way it's styled, something I don't think I've really seen much in many social spaces online (which is kinda interesting now that I think of it).