Oh, I can very much relate. There was a time when I was saying to myself "Pah, crossovers. I certainly shall never write those." You can see how well that resolution worked out.

And then it was "Well, okay, I'm writing crossovers now, but at least I'll never write real-person-fic!"

And then I wrote a real-person crossover.

Every time I say 'I AM NEVER GOING TO WRITE THAT. EVER. THAT WOULD BE INSANE', I always end up writing it. Always.