In Stephen King's "IT", the characters often say "Beep Beep Richie". At first I thought it was whenever Richie talked too much but there were other points in the book when it would be said to other characters and I never quite understood what it meant. Is there something I'm missing or is it just a silly thing they said to stop somebody from going on and on?
From what I remember, it started out as a warning to Richie that he was going over the line (or too far) with something. After a while, it became an in-joke for all of them.
I know this is an old one but for posterity...
Like @Bob Stout says, it's a way of telling Richie to stop. Around the internet, there's some talk of it being a reference to the end of a comedians stage routine in the 50s where a horn was sounded but I think it's actually a reference to the Road Runners "Meep Meep" as, when they all meet again as adults, shortly before he tells his IUD story (last part of Chapter 5); this quote appears:-
"Beep-beep, Richie," Ben said solemnly, and then exploded laughter in a hearty baritone utterly unlike his wavering childhood voice. "You're the same old roadrunner"
Perhaps saying that his mouth is running again.
It could also have something to do with the fact that Richie is scared of clowns, and most clowns have a squeaker nose. So it could be a play on his fear.