Yup. Exactly what the title says.

The situation: my GF and I want a threesome with a friend of mine. He isn't very close with either of us so he doesn't know how sexually open we are and we don't know how sexually open he is. I'm straight and he's straight. Any tips on how to go about this?

I've thought to myself "What the hell? Going up and asking directly is the probably the best thing to do," because guys aren't complicated -- and what guy is going to pass up on sex with an attractive woman? -- but I have my reservations. He may find it strange, he may think my GF is trying to cheat if she asks by herself, and other things enter my mind as negative possibilities.

Thank you for your advice!