Fact gremlin
A person who knows just enough about a topic to be smug about it but will go on forever about it, even if it's nonsense.
They told me the entire history of the Roman Empire in one sentence and then spent 10 minutes on the number of legs a spider has.
They got into a fight with a friend over whether a donut is a bread or a cake.
They told me about the first fact they learned in first grade, and then didn't stop talking about it for an hour.