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Ray of Sunshine
I hate that last one. It's worse when it's on a fancy bright color background that the text barely shows up on.Other than strictly fandom threads, the following is a hot yikes:
1. Rude vibes. I suppose this is a bit vague, but some threads give me this gut feeling that the OP will be very hard to write with. It normally shows in their responses to the thread, when others link reasonably good ideas to build a plot on that fits OP's requests, and the OP goes "I don't like it!" without giving it a chance or proposing to discuss it in PMs to see what they would like. They're dead set on something specific and shoot down potential partners right off the bat.
2. Threads with very specific, very cliche plots set in a fantasy dystopian world where sexual/physical abuse is heavily implied. I can see from a mile away that is a fantasy the OP wants to self insert themselves into. You know it when you see it. Nothing makes me nope out faster.
3. Tiny tiny font size. I'm sorry, I'm not scooting over closer to my screen to squint at size 2 text.