I think the specific, weird, niche fetish I'm into at the moment is smegma with the qualities of like a glue, with a few other things. I'll give an example: In a recent RP I did, I played a Horse while my partner played a female farmhand who though a few events ended up rimming the stinky horse I was playing. I described the horse's filthy dick getting hard, so while her character was still rimming him, she reached in-between his legs to try to stroke him only to find her hands glued to the shaft. As the horse got harder, her hands were pulled farther forward, forcing her face deeper into the horse's ass. The next part is basically what made my heart skip a beat. She said that she would wait and hope the smegma came loose, but more just started to magically build up over her hands, trapping her in that position, and in such a filthy way, forever.