My uncle Jimbo's favorite joke

Ok, reddit, this is my dear uncle Jimbo's favorite joke. Kinda long, but bear with me.
Little Eddie's class is reviewing the alphabet. His teacher knows that he has an "advanced" vocabulary for his age, so she avoids calling on him. When the teacher asks for a word beginning with "A," Little Eddie raises his hand. The teacher anticipates he'll say, "ass" so she calls on Mary Lou, who says "apple." She then asks for a word beginning with "B," and Eddie is
This continues because the teacher knows that Eddie knows a cuss word for every letter of the alphabet. Then she gets to "R." She can't think of any cuss words that begin with R, so she calls on Eddie.
He exclaims, "R is for rat. I mean a big motherfucker, with a twelve inch dick!"