Isn't it pretty obvious? You are given a movie title (in your case: The Attack of the Killer Tomatoes) and you change the title into something silly. Then you give a new movie title for the next person.
LA86 turned "Harry Potter and the goblet of fire" into " Hairy Potty and the Goblins of Shire"
"Don't complain under the stars
about the lack of bright spots in you life."
Henrik Wergeland, Norwegian writer