The funny thing about twins is that they share the same birthday. It's kind of a defining characteristic of being a twin. If you know one twin's birthday, it's nearly impossible to forget the other's. Which is exactly why u/_somethingorrather was extremely confused when he got invited to attend his twin brother's surprise birthday party. On top of that, they both share the same friend group, which makes it way weirder. OP wasn't the only confused one—close friends of the twins were baffled as t…