Huh, I also love the prompt riffing, both as a filler looking for inspiration, and as someone who'll occasionally get an idea from a prompt, but not enough for a fill. I'm more interested the reception of prompt-comments I make than my actual prompts. (Largely because I've only ever prompted a couple of things and they tend to be for more obscure ideas. But I figure you never know and maybe my kink will turn out to be someone else's kink - to answer OP's question.)

The best thing, though, is when a fill I write gets riffing in the comments section. That's my favourite thing ever.