Don't Make Me Laugh

"Don't Make Me Laugh" is a short story that was originally included alongside various food products, along with "Bad Dog" and "The Halloween Game", all of which were later collected in Goosebumps Haunted Library.

Plot
Luke and Josh love to tickle the other kids until they're begging for mercy, calling themselves the Laugh Police. They are abducted by purple aliens who have not laughed in generations, and demand the boys to use their tickling skills to make their king and queen laugh. The boys tickle the king and queen as best they can, but they appear to not be ticklish. At their failure, they're commanded to be disintegrated. Pleading for mercy, the boys begin to cry, which the aliens all find hysterical, and laugh til it hurts. The king remembers that the reason they never laugh is because it hurts too much, and again commands the boys to be disintegrated for hurting them, leaving Luke unsure whether to laugh or cry.

Trivia

 * The concept of aliens taking kids because they have an ability they think will help, only for them to be useless to them would later be used in Brain Juice.