Morrocan Seesaw 

A even lower use of the "threesome". It's when someone takes a traffic cone, shoves it up a girl's vagina. Then, she stays stiff as a board. On the "ass" side of the girl, a guy gives her anal. Another man lies on the "head" side of the girl and lies down, his erect penis along the same line of the girl's mouth. When the man on the "ass" side of the girl reaches the ground he pushes up with his legs, causing the "head" side of the girl to go down on the other guy's dick, performing a blowjob. This goes on until all three (that's important) members of the sex act cum.

If you want to find the best example to convince your guy friend to have a threesome with you and your girlfriend, the Morrocan Seesaw might want to be included as a possibility.

Morrocan Seesaw by Herm Plunkers July 8, 2006