I got sent this photo from Piggy who has a blog about exciting things he finds in science and maths. There are actually lots of fun whiteboards amongst his blog posts; for example this one about using mathematical analysis to design a strategy for hitting on the opposite sex.
In this photo, Piggy had to help a friend and explain to him the Fourier series representation of periodic and non periodic functions. He started easy, saying that Fourier had this great idea of resolving the problem in its various frequencies and then summing everything up. But then he got excited and dropped integrals here and there.