The most common term for thumbs like this is "clubbed thumbs." There's actually quite a bit about it online, although most of it is simply "Wow, Megan Fox has clubbed thumbs." It's purely inherited, and not due to sucking thumbs as a child, any type of accident, or any disease. It is not really something that can be "fixed" without finding a willing cosmetic surgeon that has experience with hands, and keeping the hands bandaged and useless for a while afterward. Who would want to deal with that? Most people with clubbed thumbs have no problems dealing with everyday life, with the exception of never being able to find properly fitting gloves.
It occours in about 2% of the general population, in most races. And a lot of people with one or both clubbed thumbs are a bit self-conscious about it, so it's kind of sad that many people here have turned it into a big joke. Both of my own thumbs are clubbed. People making fun of clubbed thumbs are the reason you don't see them in nail salons that often. We don't like to pay for people to make fun of us, we generally get that for free elsewhere.