“My wife said, ‘You’re too old to play yourself!’ How horrifying is that, especially because it’s true?” author tells TheWrap
Slight spoiler: in the film, Stine has a cameo as a high school teacher toward the end, and he bumps into "himself", who is, of course, played by Black. During their brief exchange, the movie Stine says hello to the real Stine and calls him "Mr. Black." So that's Jack Black, playing R.L. Stine, and R.L. Stine playing Mr. Black. Confusing, I know. But this actually isn't the first time a person has had a cameo in a movie in which a fictional version of themselves also appears. Here are some other examples.