1. To say foolish things; to talk of nonsense. Don't pay Jonathan any mind, Mary, he's just talking rot again.
2. To exaggerate one's achievements or knowledge of some subject; to bluff or boast. Dorothy keeps saying she can outrun anyone in our school, but she's talking rot if you ask me. It seemed like the candidate was talking rot for a while when the debate turned to the topic of tax policy and law.