What was the biggest lie you were told?

My sister told me there were two great emperors called Julius. Julius Seezer and Julius Caesar (Kazer, she pronounced it). Seezer was considered greater, but Julius Kazer conquered Britain so he was her favourite. So I end up a couple of years later in Grade 5 at primary school making an idiot of myself when I explained one conquered Britain and the other did something else.
She just constantly made stuff up and told me as if it was gospel. It took me years to work out why my knowledge of things was always wrong.