Hank I have wondered the same thing.
It sounds like he says "rust".
I'm gonna throw away your rust if you don't stop it, Derek!
"Rust" must be referencing a toy, or piece of food, or something.
Maybe someone can ask Steve at the KO3 so we can all put this to rest.
Yea and I agree about the Guiness line the daughter says...because there's no way she would come out and say something like that on her own. They were probably driving a long way, and tried thinking of cute/funny stuff to put into the film...and came up with that. It's actually one of my favorite lines from the movie...and the way Steve looks back with that odd look on his face...funny.