I did this years ago with a best friend and a girl we both had dated in the past. I'm straight and so is my buddy. The 3 of us got together one night, alcoholic drinks were imbibed and one thing led to another. It was a lot of fun. DP, and all kinds of other positions. It just kind of happened naturally. The weird thing is, none of us have ever talked about it since.
Bottom line (no pun intended) I'd be up (pun intended) for doing it again sometime.