I read this one quite a while ago, so the details are a little sketchy.
It was an AU where I think Dean was on a Baseball team, with an established relationship with Cas, who none of the team had met so assumed he was female. Dean brought in lemon cakes and stuff from him, then at a match he tells the Team that Cas is coming and when they see Dean kissing some dude as opposed to his girlfriend they're kinda surprised. It's a very happy-go-lucky fic. Ring any bells?

Found in comments!