I believe he is referring to you no knowing much about "It". I mean, you may know and have forgotten or just didn't make the connection. But I don't think he was saying you don't know what a balloon is... or maybe he was... But I read it like I explain. Hope this helps...
Much about what?
Revelation34 posted...
It's just a joke comment aimed at him not watching movies for like 30 years.
20 years next year. Oh! You mean It with a capital I, as in that clown movie. Clowns like balloons...
IT was also a book. the original movie came out in 1990
Something like that. Not that I get how it relates to the whole sewer balloon prank so that musta been part of the movie.