I'll never write a story about some particular bloodline having an inherent right to... well, anything. People in my stories may believe that, often strongly, but I won't write it as truth. (Curiously, I'll readily curse a bloodline, but that's usually due to inbreeding or breeding outside the species.)
Similarly, The Chosen One. Harry Potter would have died early on in my stories. Hermione and Neville would have led the resistance, and they would have wrapped it up in record time.
Another one for me is teenage love triangles. As it is, I'm staring straight down the barrel of one. Gotta defuse it, and quick.
Still, I'm not sure that it really counts as a love triangle if it's just common teenage romances that go round and round for a while, then just stop.
(And don't even get me started on soulmates... ugh!)