I apologize for the "softness" of this enquiry, but as mathematics educators I believe these are some of the most rewarding moments of teaching our discipline. Having said that, may I share with you a story of teaching an online high school student elementary Algebra, after which, I replied "thanks for trying to learn", the student answered, "I always try before I give up." :D
I am simply looking for stories, to share with other mathematics educators, that made them laugh out loud. This, imho, is part of the reward in teaching.