Like JJT, I'm gonna say writing long-winded submissions emails, especially when they don't deliver the goods. I don't need a dissertation, just a few thoughts about your approach.
Another thing I really hate is when someone sends us a mix and tries to use some self-deprecating-reverse-psychology bullshit on us by saying "This probably won't get accepted anyway, but I figured I'd send it your way to get some feedback." Sorry, but we're not the WIP forum. We evaluate remixes for the site, not for your personal improvement. If you don't honestlybelieve that your remix is going to get accepted to the site, don't submit it. Every time I've been rejected from OCR (something that hasn't happened in years, but that's beside the point), I've been surprised. I have confidence in every submission I make, and if I make a remix that I don't believe would be posted to OCR, I don't submit it. It doesn't make me any less of an artist.
One last pet peeve: if you submit a song to OCR, don't use your submission email to editorialize about how you think the submissions process is full of shit, or how certain judges lack "credentials." That's just rude, and while we always strive to judge the music and not the person, that kind of bullshit is a quick ticket to a glib vote.