This guy is nearing the end of his senior year in high school, unfortunately he still has to share a room with his younger brother who is about 5 or 6.
One night, he decides to bring his girlfriend home for a little fun. They have bunk beds and the guy notices that his little brother is already asleep on the lower bunk, so he and his gal climb up to the top bunk.
As you might expect things start to heat up. The guy remembering that his little brother is sleeping below so he tells his girlfriend to whisper,"lettuce" if she wants it harder and "tomato" if she wants a new position.
"Lettuce, tomato, lettuce, tomato, lettuce, lettuce," it sounds.
Then the little brother chimes in, "Hey, would you guys stop making sandwiches up there, you're getting mayonnaise all over my face."