Ooh, good question! I think mine is where there's absolutely no lead up to the relationship. In canon, they loathed each other (at least until the Manor scene in DH). In so many fics, they force the point of mutual hatred at every turn, then have D & H kissing and frotting without any natural progression. Not that angry!sex turns me off, but that it just "pops up" without anything to support such a plot turn.

Guess that's why I like your fics so much-- the evolution of their relationship makes sense!!!