Say this when you're caught sleeping in the classroom:
Teacher: Mr/Ms ____, must you fall asleep while I'm speaking?
Student: No Ma'am, it's purely voluntary.
This witty response is attributed to British politician and WWII leader Winston Churchill when he was dozing off at a meeting. Note that the teacher has to say something along the line above, or the response will be out of place.
(img thanks to jeanchoi)
