Threesome -- Fast forward through almost any porn movie, and a threesome seems like a fine way for drunken neighbors, bored coeds or PTA members to pass the time.

While this may seem like an impossible fantasy, for some guys a threesome isn't attainable only by rental or download. A lucky few make this dream come true with a combination of planning, seduction and birthday-wish begging.

We asked sex therapist Ian Kerner, author of "She Comes First," to tell us how to pull off this horny hat trick without anyone getting hurt. Be warned: It isn't as easy as the "Double Pom-Pom Parade" would have you believe, and there are risks you may not expect.