A male with an erection, lies on his back while a second erect male inserts the penis of the first into his anus then lies back. A third male inserts the penis of the second into his anus and lies back forming a stack. A three man stack is known as a short stack, A stack of four or more is known as a full stack. Full stacking has the added benefit of asphyxiating the bottom participants. The flapjacking experience can be enhanced by using maple syrup as lube and having each participant massage the balls of the person above.
Mark, Mike, Jason and Joel were planning a full stack flapjacking session last night but Joel didn't show, so the three had to make do with a short stack.