When I tell people that I am a organic chemist they either think I work in a farmacy or that I am a hippy above my station. But what it really means it that I work with carbon containing compounds.The perfect reaction to show the carbon contained within these compounds is the dehydration of sugar using H2SO4. When the two are mixed the mixture turns yellow, then brown, then black. A large column of carbon is then expelled from the beaker.
(C12H22O11 → 12 C + 11 H2O) This experiment also happens to be the first chemistry experiment I saw in school.