My original concept was aimed at a picture book for very young children, (thus no real use for the love interest) but I think this is going to end up a novel. At the moment I'm thinking it will be aimed at the pre-teen audience, but that could change again. In any case, I was thinking along those lines, and when she said it, it seemed pretty clear what was missing.
Aw, crud. After I typed this post, I thought I'd better look around and see whether my tagline is in use in other places. Apparently, "Worst Pirate Ever" is a popular t-shirt by Roman Dirge. It seems that there's no book or graphic novel to go along with it, though, just a great image of a pirate skeleton that has clearly met with misfortune. My idea doesn't involve skeletons or the like, and it's a full story--I'm thinking novel--so I think I can safely say it doesn't infringe on his work at all. And apparently there's a line in Pirates of the Caribbean where one character says to another, "You are, without a doubt, the worst pirate I've ever seen in my life." I don't remember it, but OK. It's out there. I don't see how my story could infringe on it, since none of the other elements of POTC are in there except humor and pirates.
I can actually think of a way or two to do the story without that phrase, but that was what popped into my head to get the whole thing rolling.