cocaine in movies

In many movies I’ve seen, a character snorts lines of coke on a mirror. Why a mirror? Is it some kind of symbolic thing or does it reflect (pun intended) on a real life custom?

A smooth surface would be the best choice for cutting “lines” (i.e. forming small lines of powder with a razor blade prior to snorting with a straw or rolled-up dollar bill) and a glass tabletop would be the best choice.

As for the mirror, it makes you look like you got more blow, man!