In imperial China the government divided civil positions into nine ranks, and jipin was the highest. Literally "极品" (jípǐn) means something like "the supreme rank." Casually, the word was used to describe anything that was really high-class.
But today, jipin is used to refer to a person who is exceptionally annoying and gifted when it comes to driving others crazy. For example, if your boss consistently comes up with cruel, menial tasks for you, you could call him jipin (but, of course, not to his face). Or if your next door neighbors seem to knock on your door daily with inexplicable complaints, they're jipin.
Just remember, don't use this word unless the person really deserves it. If you meet someone with just a mediocre degree of annoyance, or someone you dislike simply because they're boring—don't say jipin, it would diminish the impact of the word.