Noun: An appropriate rhythm while stitch-fucking. Two males are double penetrating a woman in her anus and vagina, and as one goes in, the other is going out. This appropriate rhythm ensures that the woman is fully penetrated at all times and does not die or get split in half. This also conveniently prevents the two men's testicles from touching each other, which could call their heterosexuality into question.
Matt: Man, when I grow up, I want to be just like Josh and Stacy. They're masters of synchronized stitch. All the chicks are talking about them.
Zack: Yeah, I hear their balls don't even touch. They're gonna turn synchronized stitch into an Olympic sport!