Kalyn: Mrs. Frizzle,
Mrs. Frizzle: Sure.
Kalyn: Can you spell I-C-U-P for me?
Mrs. Frizzle: Shut up, you little fucktard!
Listen up, dummy! You are a disgrace! The joke plays on how "ICUP" sounds like "I see you pee." Kalyn is tryna trick Mrs. Frizzle into saying "I see you pee," but Mrs. Frizzle ain't fallin' for that childish prank and instead insults Kalyn.