Mathematics can even be a matter of life or death. During the Russian revolution, the mathematical physicist Igor Tamm was seized by anti-communist vigilantes at a village near Odessa where he had gone to barter for food. They suspected he was an anti-Ukranian communist agitator and dragged him off to their leader.(via a commenter on Political Animal...)
Asked what he did for a living he said that he was a mathematician. The sceptical gang-leader began to finger the bullets and grenades slung around his neck. "All right", he said, "calculate the error when the Taylor series approximation of a function is truncated after n terms. Do this and you will go free; fail and you will be shot". Tamm slowly calculated the answer in the dust with his quivering finger.
When he had finished the bandit cast his eye over the answer and waved him on his way.
Tamm won the 1958 Nobel prize for Physics but he never did discover the identity of the unusual bandit leader. But he found a sure way to concentrate his students' minds on the practical importance of Mathematics!
On a side note, I would never have dreamed of seeing Mean Girls, but computing a limit in one's head in 20 seconds ....