Curious because I'm a freak who needs ideas for a fic, what are your favourite A/B/O tropes and why?

I don't know what else to say other than I finally have the motivation to write, but I have zero ideas and just want to write some good old Omegaverse to see if I can get myself in the mood... to write my horribly angsty fic that I haven't even posted the first chapter to xD

Whatever tropes you want to share can be shared! Freaky, worldbuilding, non-freaky, fluffy... I don't give a shit, I just want to hear them!