Numquam ubi sub ubi

Latin/English sound pun. The direct translation from Latin to English is "Never where under where." When spoken it comes out as "Never wear underwear." The phrase follows the natural progression of sweet freshman Latin students to their randy senior counterparts and is derived from Semper ubi sub ubi.

Teacher: Semper ubi sub ubi!
Class: Numquam ubi sub ubi!
Teacher: Numquam??? Oh good grief!
Class: <hilarity ensues>
Teacher: Settle down class!