Making sandwiches - Sex Jokes

A boy says to a girl, "So, sex at my place?" "Yeah!" "Okay, but I sleep in a bunk bed with my younger brother, and he thinks we're making sandwiches, so we have to have a code. Cheese means faster and tomato means harder, okay?" Later on the girl is yelling, "Cheese cheese, tomato tomato!" The younger brother says, "Stop making sandwiches! You're getting mayo all over my bed!"