I have heard a few of these "Little Johnny" jokes, whereby a teacher asks something innocuous of him, and he replies with something vulgar. The jokes involve some misuse of words. For instance, the teacher might ask him to use the word "field" in a sentence, and Johnny might reply about how he "feeled" his balls or some such.
Little Johnny goes to school, and the teacher says, 'Today we are going to learn multi-syllable words, class. Does anybody have an example of a multi-syllable word?'
Little Johnny waves his hand, 'Me, Miss Rogers, me, me!'
Miss Rogers:'All right, little Johnny, what is your multi-syllable word?'
Little Johnny says, 'Mas-tur-bate.'
Miss Rogers smiles and says, 'Wow, little Johnny, that's a mouthful.'
Little Johnny says, 'No, Miss Rogers, you're thinking of a blowjob".