Rain Man was a movie about a guy who discovers his long lost autistic brother is a math savant, and plans to take advantage of his abilities for gambling purposes. He comes to realize that he actually cares about his brother, and takes care of him, rather than exploiting him. The title comes from the fact that the guy's only memory of his brother was from early childhood, when he couldn't pronounce his autistic brother Raymond's name, so called him 'Rain Man'.

So, your mother is saying you sound like you're autistic, which isn't very nice. She most likely means that you sound obsessive and recite facts frequently, which means you are a reptile geek like the rest of us here. You might try asking her if she would rather you were reciting sports statistics, and ask her if she has anything SHE really loves to do and talk about. (Most folks have a hobby that they are passionate about, after all).

In your place, I would remind her that there are worse things to be passionately interested in, after all.