Poorly written female characters that exist for the RPer to force a romantic subplot into the story have always bugged me. Actually, when I was younger and not polite, I'd literally write that my OC hated their OC so there wouldn't be any misgivings. To me, it's buying into regressive notions of femininity and has become a trope.
For the same reason I tend to avoid romance all together. Some people fetishize homosexuality and it's a little... offensive, frankly. Especially with the seme/uke subculture that has some noncon peppered throughout. And this is speaking as someone who used to love that kind of stuff. I'm glad that I matured enough to see how problematic it is.
I think what bugs me the most though are partners that will provide their own ideas for an RP, but won't ask you for yours. It's like they're assuming you'll have nothing to add or offer.