I read cozy and historical mysteries, a bit of Paranormal/UF, and to mix it up, I read science and gardening books on occasion.
Most irritating character in a novel - that's a wide open field, truly. Many novels great and small immediately came to mind, including one cozy series I stopped reading altogether because one of the characters was just abusive. But I have to go with my first choice; the first character that popped into my head when I read today's entry.
Mrs. Norris. An odious woman who almost single-handedly brings down an entire family, all while trying to appear to do right. Emphasis on appear.
Jane Austen's wrote some truly irritating characters, but Mrs. Norris is the one that spikes my blood pressure.