Favoute fanfiction cliché/trope?

[lucre-noin.livejournal.com]

I am as curious as awlays and I was wondering what kind of fanfiction cliché/trope you prefer to read. I guess a cliché or a trope can be a certain situation that is used in more than a couple of fanfictions and that comes directly from situations from the different universes (comics, movies etc.)

For example, I have a special preference for the classic "Steve doesn't know that Tony is Iron Man" and I adore also the "Steve and Tony goes on dates but Tony doesn't know they are dating".