Turtle Sandwhich 

It is the process of 3 or more turtles mating at the same time. So pretty much a turtle orgy.

"Look at all of those turtles stacked on top of each other, they look like a Turtle Sandwhich and sound like one in the making. Ew."

Turtle Sandwhich by Mitkish September 12, 2014

Japanese Turtle Sandwich 

When a man massages a woman's labia minora slowly with his tongue. This is said to be a "turtle sandwich" because the man is "eating-out" the woman slowly (like a turtle would). The Japanese root of this phrase is there because Japanese people have a strong affiliation with turtles, especially in their diet.

Wegner (Teacher) - You're expose is late! You're getting an F this quarter!
Young Student - NO PLEASE! I'll do anything!!
Wegner (Teacher) - Even... a Japanese Turtle Sandwich?
Young Student - (gulps)... Yes! Even that!

(the process follows)

Japanese Turtle Sandwich by Franco P. December 14, 2008