I have one particularly strange one...I like to call it "portaling." It's where one character uses magical or highly technologically advanced-depending on the setting-devices to separate body parts (typically ones of a naughty nature) without pain or gore, for some purpose or another. Preferably with the part still functioning as normal in every way, including sending sensory input back to its owner. Like, there was this one RP I did (not on this site, obviously) where my character would take guys' dicks home with her to use like dildos. I dunno' why, but the whole concept's really hawt to me.
Oh, and another that's not so much weird as...kind of niche, I guess? But I also really like cubs/lolis/what-have-you practicing "the world's oldest profession" (quotation marks because it almost definitely isn't...) or else getting married to adults. But that's also one I can't really explain, I just enjoy it. ^_^;
Updated by anonymous