The appeal of the contest is not just to have Marc Okrand like your sentence, but also to make it canonical Klingon. Part of the conceit of those proverbs is that there's a small, closed set of canonical ones that you're supposed to use rather than just inventing one on the spot. On the other hand, insults, toasts, and the like don't need to be canonized to be used or understood properly. There are known examples, but you can also just make one up. A better equivalent might be a contest to invent a new canonical idiom or slang word, although it would probably be harder to judge.