Can't Think Of An N-Word

In Improv workshop class last night, we played the 'Alphabet Game', wherein two actors improvise a scene with dialogue that must start in alphabetic order (Person 1 starts with the letter 'A'; Person 2 with 'B', Person 1 with 'C', etc.)

I became tongue-tied at the letter 'N'. As I departed the stage I told one of the actors (an African-American) that "I can't think of an N-word." He laughed unusually hard about that.