Elder brother and his girlfriend

There are two siblings.
A little brother and a big brother.
Now, the big brother had a girlfriend, and one night they decided to go and have sex.
So, the bigger brother goes to pick up his girlfriend one night, and take her home.
So they get to the bigger brothers house, and walk in his room.
Now the two siblings shared the room, and they had bunk bed. W
hen they walked in the room, they saw the little brother asleep in the bottom bunk, so they went up to the top bunk to have sex.
The big brother says, “whenever you feel good, say lettuce, and whenever you want to switch positions say tomato.” The girl constantly is saying “lettuce, tomato” and then the little brother wakes up.
He quietly remarks, ” can you guys stop making sandwiches, you’re getting mayonnaise all over me.