Another new guy walks in and finds this friendly group explaining how they joke by number. They encourage him to give it a try and he enthusiastically says "18

Another new guy walks in and finds this friendly group explaining how they joke by number. They encourage him to give it a try and he enthusiastically says "18". Nobody laughed at all. Crickets. He asks the guy next to him, "isn't 18 funny?" "Yes, but you have to know how to tell a joke."